[bazel] Update tblgen rules to support path-mapping (#158354)

Path mapping is a feature of bazel that allows actions to be
deduplicated across bazel transitions if they are otherwise identical.
This is helpful if you build a binary in N transitions, where the
settings differences are irrelevant to this action. In our case we build
multiple python native extensions transitioning on the python version
they target, and before this change would run each of these actions once
per python version even though the outputs would be identical.

This is a no-op unless `--experimental_output_paths=strip` is passed.

The changes here are just enough to make bazel automatically remap the
paths, which is done by how you use the args object. The core change is
that instead of carrying around paths that have `ctx.bin_dir` hardcoded
in the strings. This is done by mapping them with the output file
object's root path when adding them to the args.

As a side effect this drops the genfiles_dir, but that has been the same
as bin_dir for a long time so hopefully that's a no-op for folks.

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