Rollup merge of #139075 - oli-obk:resolver-item-lifetime, r=compiler-errors

Do not treat lifetimes from parent items as influencing child items

```rust
struct A;
impl Bar<'static> for A {
    const STATIC: &str = "";
    //            ^ no future incompat warning
}
```

has no future incompat warning, because there is no ambiguity. But

```rust
struct C;
impl Bar<'_> for C {
//       ^^ this lifeimte
    const STATIC: &'static str = {
        struct B;
        impl Bar<'static> for B {
            const STATIC: &str = "";
            // causes     ^ to emit a future incompat warning
        }
        ""
    };
}
```

had one before this PR, because the impl for `B` (which is just a copy of `A`) thought it was influenced by a lifetime on the impl for `C`.

I double checked all other `lifetime_ribs` iterations and all of them do check for `Item` boundaries. This feels very fragile tho, and ~~I think we should do not even be able to see ribs from parent items, but that's a different refactoring that I'd rather not do at the same time as a bugfix~~. EDIT: ah nevermind, this is needed for improving diagnostics like "use of undeclared lifetime" being "can't use generic parameters from outer item" instead.

r? `@compiler-errors`

Author: matthiaskrgr