Bug: ProguardMapping is not queryable nor deterministically generated

There is a bug in rules_android where the proguard_mapping file may not be reproduced. The root cause is that the proguard mapping file is not being explicitly declared as the output of the implicit target.

### Reproduction steps:

1) Build a Bazel binary that enables proguard mapping, enables disk, and remote cache
2) Run bazel clean --expunge
3) Rebuild the Bazel binary.
4) Observe the proguard mapping is not found at bazel-out/xplat-fastbuild/bin//_RESOURCES_DO_NOT_USE_proguard.map

Furthermore, there is no way to actually query this file. This is problematic because we will need to upload the obfuscated mapping when debugging/deobfuscating builds.

bazel cquery //:_RESOURCES_DO_NOT_USE --output files