…ors (#32520)

See newly added test fixtures. Repros fixed in later prs of this stack
---
[//]: # (BEGIN SAPLING FOOTER)
Stack created with [Sapling](https://sapling-scm.com). Best reviewed
with [ReviewStack](https://reviewstack.dev/facebook/react/pull/32520).
* #32522
* #32521
* __->__ #32520

Array and argument spreads may mutate stateful iterables. Spread sites
should have `ConditionallyMutate` effects (e.g. mutate if the ValueKind
is mutable, otherwise read).

See
- [ecma spec (13.2.4.1 Runtime Semantics: ArrayAccumulation.
SpreadElement : ...
AssignmentExpression)](https://tc39.es/ecma262/multipage/ecmascript-language-expressions.html#sec-runtime-semantics-arrayaccumulation).
- [ecma spec 13.3.8.1 Runtime Semantics:
ArgumentListEvaluation](https://tc39.es/ecma262/multipage/ecmascript-language-expressions.html#sec-runtime-semantics-argumentlistevaluation)

Note that
- Object and JSX Attribute spreads do not evaluate iterables (srcs
[mozilla](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/Spread_syntax#description),
[ecma](https://tc39.es/ecma262/multipage/ecmascript-language-expressions.html#sec-runtime-semantics-propertydefinitionevaluation))
- An ideal mutability inference system could model known collections
(i.e. Arrays or Sets) as a "mutated collection of non-mutable objects"
(see `todo-granular-iterator-semantics`), but this is not what we do
today. As such, an array / argument spread will always extend the range
of built-in arrays, sets, etc
- Due to HIR limitations, call expressions with argument spreads may
cause unnecessary bailouts and/or scope merging when we know the call
itself has `freeze`, `capture`, or `read` semantics (e.g.
`useHook(...mutableValue)`)
We can deal with this by rewriting these call instructions to (1) create
an intermediate array to consume the iterator and (2) capture and spread
the array at the callsite
---
[//]: # (BEGIN SAPLING FOOTER)
Stack created with [Sapling](https://sapling-scm.com). Best reviewed
with [ReviewStack](https://reviewstack.dev/facebook/react/pull/32521).
* #32596
* #32595
* #32594
* #32593
* #32522
* __->__ #32521

…ties (#32593)

Expand type inference to infer mixedReadOnly types for numeric and
computed property accesses.
```js
function Component({idx})
  const data = useFragment(...)
  // we want to type `posts` correctly as Array
  const posts = data.viewers[idx].posts.slice(0, 5);
  // ...
}
```
---
[//]: # (BEGIN SAPLING FOOTER)
Stack created with [Sapling](https://sapling-scm.com). Best reviewed
with [ReviewStack](https://reviewstack.dev/facebook/react/pull/32593).
* #32596
* #32595
* #32594
* __->__ #32593
* #32522
* #32521

- Add `at`, `indexOf`, and `includes`
- Optimize MixedReadOnly which is currently only used by hook return
values. Hook return values are typed as Frozen, this change propagates
that to return values of aliasing function calls (such as `at`). One
potential issue is that developers may pass
`enableAssumeHooksFollowRulesOfReact:false` and set
`transitiveMixedData`, expecting their transitive mixed data to be
mutable. This is a bit of an edge case and already doesn't have clear
semantics.
---
[//]: # (BEGIN SAPLING FOOTER)
Stack created with [Sapling](https://sapling-scm.com). Best reviewed
with [ReviewStack](https://reviewstack.dev/facebook/react/pull/32594).
* #32596
* #32595
* __->__ #32594
* #32593
* #32522
* #32521

(see title)
---
[//]: # (BEGIN SAPLING FOOTER)
Stack created with [Sapling](https://sapling-scm.com). Best reviewed
with [ReviewStack](https://reviewstack.dev/facebook/react/pull/32522).
* #32596
* #32595
* #32594
* #32593
* __->__ #32522
* #32521

DiffTrain build for [38a7600](38a7600)

Move all gating tests to `gating/`
---
[//]: # (BEGIN SAPLING FOOTER)
Stack created with [Sapling](https://sapling-scm.com). Best reviewed
with [ReviewStack](https://reviewstack.dev/facebook/react/pull/32595).
* #32596
* __->__ #32595
* #32594
* #32593
* #32522
* #32521

Array and argument spreads may mutate stateful iterables. Spread sites
should have `ConditionallyMutate` effects (e.g. mutate if the ValueKind
is mutable, otherwise read).

See
- [ecma spec (13.2.4.1 Runtime Semantics: ArrayAccumulation.
SpreadElement : ...
AssignmentExpression)](https://tc39.es/ecma262/multipage/ecmascript-language-expressions.html#sec-runtime-semantics-arrayaccumulation).
- [ecma spec 13.3.8.1 Runtime Semantics:
ArgumentListEvaluation](https://tc39.es/ecma262/multipage/ecmascript-language-expressions.html#sec-runtime-semantics-argumentlistevaluation)

Note that
- Object and JSX Attribute spreads do not evaluate iterables (srcs
[mozilla](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/Spread_syntax#description),
[ecma](https://tc39.es/ecma262/multipage/ecmascript-language-expressions.html#sec-runtime-semantics-propertydefinitionevaluation))
- An ideal mutability inference system could model known collections
(i.e. Arrays or Sets) as a "mutated collection of non-mutable objects"
(see `todo-granular-iterator-semantics`), but this is not what we do
today. As such, an array / argument spread will always extend the range
of built-in arrays, sets, etc
- Due to HIR limitations, call expressions with argument spreads may
cause unnecessary bailouts and/or scope merging when we know the call
itself has `freeze`, `capture`, or `read` semantics (e.g.
`useHook(...mutableValue)`)
We can deal with this by rewriting these call instructions to (1) create
an intermediate array to consume the iterator and (2) capture and spread
the array at the callsite
---
[//]: # (BEGIN SAPLING FOOTER)
Stack created with [Sapling](https://sapling-scm.com). Best reviewed
with [ReviewStack](https://reviewstack.dev/facebook/react/pull/32521).
* #32596
* #32595
* #32594
* #32593
* #32522
* __->__ #32521

DiffTrain build for [ed1264f](ed1264f)

…ties (#32593)

Expand type inference to infer mixedReadOnly types for numeric and
computed property accesses.
```js
function Component({idx})
  const data = useFragment(...)
  // we want to type `posts` correctly as Array
  const posts = data.viewers[idx].posts.slice(0, 5);
  // ...
}
```
---
[//]: # (BEGIN SAPLING FOOTER)
Stack created with [Sapling](https://sapling-scm.com). Best reviewed
with [ReviewStack](https://reviewstack.dev/facebook/react/pull/32593).
* #32596
* #32595
* #32594
* __->__ #32593
* #32522
* #32521

DiffTrain build for [eb53139](eb53139)

- Add `at`, `indexOf`, and `includes`
- Optimize MixedReadOnly which is currently only used by hook return
values. Hook return values are typed as Frozen, this change propagates
that to return values of aliasing function calls (such as `at`). One
potential issue is that developers may pass
`enableAssumeHooksFollowRulesOfReact:false` and set
`transitiveMixedData`, expecting their transitive mixed data to be
mutable. This is a bit of an edge case and already doesn't have clear
semantics.
---
[//]: # (BEGIN SAPLING FOOTER)
Stack created with [Sapling](https://sapling-scm.com). Best reviewed
with [ReviewStack](https://reviewstack.dev/facebook/react/pull/32594).
* #32596
* #32595
* __->__ #32594
* #32593
* #32522
* #32521

DiffTrain build for [89a46a5](89a46a5)

…iers (#32596)

Reduce false positive bailouts by using the same
`isReferencedIdentifier` logic that the compiler also uses for
determining context variables and a function's own hoisted declarations.

Details:
Previously, we counted every babel identifier as a reference. This is
problematic because babel counts most string symbols as an identifier.

```js
print(x);  // x is an identifier as expected
obj.x      // x is.. also an identifier here
{x: 2}     // x is also an identifier here
```

This PR adds a check for `isReferencedIdentifier`. Note that only
non-lval
references pass this check. This should be fine as we don't need to
hoist function declarations before writes to the same lvalue (which
should error in strict mode anyways)
```js
print(x);  // isReferencedIdentifier(x) -> true
obj.x      // isReferencedIdentifier(x) -> false
{x: 2}     // isReferencedIdentifier(x) -> false
x = 2      // isReferencedIdentifier(x) -> false
```
---
[//]: # (BEGIN SAPLING FOOTER)
Stack created with [Sapling](https://sapling-scm.com). Best reviewed
with [ReviewStack](https://reviewstack.dev/facebook/react/pull/32596).
* __->__ #32596
* #32595
* #32594
* #32593
* #32522
* #32521

…iers (#32596)

Reduce false positive bailouts by using the same
`isReferencedIdentifier` logic that the compiler also uses for
determining context variables and a function's own hoisted declarations.

Details:
Previously, we counted every babel identifier as a reference. This is
problematic because babel counts most string symbols as an identifier.

```js
print(x);  // x is an identifier as expected
obj.x      // x is.. also an identifier here
{x: 2}     // x is also an identifier here
```

This PR adds a check for `isReferencedIdentifier`. Note that only
non-lval
references pass this check. This should be fine as we don't need to
hoist function declarations before writes to the same lvalue (which
should error in strict mode anyways)
```js
print(x);  // isReferencedIdentifier(x) -> true
obj.x      // isReferencedIdentifier(x) -> false
{x: 2}     // isReferencedIdentifier(x) -> false
x = 2      // isReferencedIdentifier(x) -> false
```
---
[//]: # (BEGIN SAPLING FOOTER)
Stack created with [Sapling](https://sapling-scm.com). Best reviewed
with [ReviewStack](https://reviewstack.dev/facebook/react/pull/32596).
* __->__ #32596
* #32595
* #32594
* #32593
* #32522
* #32521

DiffTrain build for [f457d0b](f457d0b)