Merge changes Ib1a1d1bb,If0362c6d,I6018791a,Id81c93ea,I7704a884, ...

* changes:
  Create a filegroup for public stub sources
  Minor refactorings in api.go
  Convert merged module lib stub to api.go
  Some minor tweaks for api.go
  Temporarily add support for conditional modules
  Construct sdk-annotations.zip programmatically
  Replace manual genrule modules with combined_apis