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