Implement namespaced R classes

[jongerrish]

Enable rudimentary R class namespacing where each library only contains
references to the resources it declares instead of declarations plus all
transitive dependency references.

This basically implements the android.namespacedRClass=true Gradle feature in Bazel.

For our build this saves a total of 215MB outputs + 145 Actions for a clean build in addition to previous open PRs.

No resource merging for android_library targets
Smaller R.{class,txt}
Less desugaring + dexing

[jongerrish]

@jin

[jin]

cc @donaldchai @timpeut @djwhang

[ulfjack]

Not much progress here. Anyone willing to make a decision here? If Google isn't using these rules internally, maybe someone from the community can take over responsibility for reviews (but would require a Googler to merge)?

[Bencodes]

It's been a while since there have been any updates here. Could someone make a call here?

[nkoroste]

Any updates on this?

[ahumesky]

Closing this one in favor of the Starlark version of this issue: bazelbuild/rules_android#66