Allow declaring new private attributes when inheriting in a symbolic macro

[joca-bt]

Description of the feature request:

When defining a symbolic macro based on an existing rule or macro and using attribute inheritance, it's not possible to add a new attribute not present in the rule or macro being inherited.

Adding new attributes may be useful, particularly if they're private. For example, let's say I'm wrapping java_test to use my own test runner. I imagine the ideal way to provide my test runner to the macro is via a private atribute, similary to how we would do it if we were defining a rule:

my_test_wrapper = macro(
    inherit_attrs = java_test,
    attrs = {
        ... // block some attributes via None
        "_test_runner": attr.label(
            default = "//test-runner",
            allow_single_file = True,
        ),
    },
    ...
)

Error: no such attribute '_test_runner' in 'java_test' rule (did you mean 'use_testrunner'?)

While I can understand adding public attributes could not be desired, I think allowing private attributes can be very useful.

Which category does this issue belong to?

Rules API

What underlying problem are you trying to solve with this feature?

Creating more powerful macros.

Which operating system are you running Bazel on?

WSL

What is the output of bazel info release?

release 8.0.0

If bazel info release returns development version or (@non-git), tell us how you built Bazel.

No response

What's the output of git remote get-url origin; git rev-parse HEAD ?

Have you found anything relevant by searching the web?

No response

Any other information, logs, or outputs that you want to share?

No response