Generate module lib API and scope together

Previously, due to limitations in metalava the module lib API and stubs
source were generated separately. That limitation has since been
removed so this change optimizes the generating code.

Changes:
* Add an annotation field to apiScope to contain the annotation that
  identifies the scope.
* Rename droidstubArgs to extraArgs to better reflect that they are not
  passed to droidstubs.
* Rename droidstubsArgsForGeneratingStubsSource to droidstubsArgs.
* Remove droidstubsArgsForGeneratingApi and
  createStubsSourceAndApiTogether fields along with code that supports
  generating stubs source and the API separately.
* Fix the module lib test.

Test: m checkapi
Bug: 161364853
Change-Id: I821886bb68645addf5ae9c96ed2f4f3649151d1a