java_sdk_library: Control API surfaces generated

Adds a per scope set of properties that allows explicit control over
the API surfaces generated.

Previously, the term active was used to determine whether it was
generated but that was a little abstract and unclear so has been
replaced by generated.

Test: m nothing
Bug: 155164730
Change-Id: I7539d89618b61f6b9d1a4b60cc3f9614b157f0d9