importlib.metadata.files() doesn't work because RECORD is missing

It appears that `importlib.metadata.files()` is broken with the pypi integration because the RECORD file gets ommited.

Per docs at https://docs.python.org/3/library/importlib.metadata.html#distribution-files

> In the case where the metadata file listing files (RECORD or SOURCES.txt) is missing, files() will return

This came to my attention via @mering trying to use the rtree package, which tries to use its distribution metadata to find some C libraries to load.

Excluding RECORD seems somewhat intentional, though? The code has this comment:

https://github.com/bazel-contrib/rules_python/blob/main/python/private/pypi/whl_library_targets.bzl#L315-L318

> RECORD is known to contain sha256 checksums of files which might include the checksums
> of generated files produced when wheels are installed. The file is ignored to avoid
> Bazel caching issues.

What's the caching issue, exactly? For a downloaded whl, what generated files is it referring to? If a whl is built at repo time from an sdist, then files shouldn't be changing, and the hash should be stable, so how does a cache issue come up?

Start with the RECORD omission comment in python/private/pypi/whl_library_targets.bzl around lines 315-318, then compare it with the importlib.metadata.files() documentation and the rtree use case described here. Determine the caching concern and whether the PyPI integration should preserve RECORD so files() works; done means the behavior and resolution are documented or implemented with validation.

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