Macro visibility attribute missing from stable Bazel 8.0 starlark_doc_extract proto output.

[tetromino]

Bazel 8.0 is expected to not have the macro visibility attribute in starlark_doc_extract proto output - we didn't quite make the cutoff.

My current plan is to inject one in stardoc's .md renderer, since it's quite critical for documenting macro behavior. But we should stop injecting once the stable Bazel release has the correct proto output