Generate documentation for module extensions

[ylecornec]

Stardoc does not seem to handle module extensions yet: https://github.com/bazelbuild/stardoc/issues/123

[avdv]

Support for module extensions landed in stardoc 0.6.0 but is only supported by Bazel >= 7 as of now:

When using Bazel 7 or newer (or current Bazel HEAD), Stardoc will by default use the native starlark_doc_extract rule internally (https://github.com/bazelbuild/stardoc/pull/166).

This means, in particular:

• correct default values for rule attributes in all cases
• documentation for module extensions
• more complete documentation for repository rules
• by default (this can be turned off via render_main_repo_name = False), we will render labels in your main repo with a repo component: your main module name (when using bzlmod) or WORKSPACE name (https://github.com/bazelbuild/stardoc/pull/168).

You may temporarily disable the new extractor by calling Stardoc with use_starlark_doc_extract = False. However, after Bazel 7 is released, we plan to remove this argument and always use the new extractor.