Initial bp2build converter for android_app.

The only supported attributes at this point are:
- srcs
- manifest
- package_name
- resource_dirs
as they most easily map to bazel's android_binary's srcs, manifest, custom_package, and resource_files respectively.
Allow-listing all apps that use these fields, along with sdk_version and dex_preopt. The latter 2 are ignored by the converter,
- sdk_version because we're currently relying on a single pre-built SDK,
- dex_preopt because,
   1. though it is not supported in Bazel builds yet, it doesn't prevent the apps from building, and
   2. the apps being converted only use the dex_preopt attribute to disable dex_preopt, which is what is happening anyway.

Change-Id: I4a4f771eeb8f60a1cd4844b2ac1ce3df7c070e73
Test: ./build/bazel/scripts/run_presubmits.sh
Bug: 198224074
Bug: 203688791