apex_manifest in protobuf binary format

For Q compatibility, .json files are also bundled.

Three different apex_manifest files are built from input.
- apex_manifest.json: Q-readable .json file
- apex_manifest_full.json: input + dependency
- apex_manifest.pb: apex: converted from apex_manifest_full.json

apexer will handle these files.

Bug: 143654022
Test: m
Change-Id: I9697094057f0c0543282b1b46b7535cf21431176