Include annotations in module metalava runs

Without this, we don't get nullability annotations in the stub sources,
nor the stubs themselves, which is a requirement for good interop with
kotlin.

Bug: 157010342
Test: m
Test: javap -c -v out/soong/.intermediates/frameworks/base/apex/media/\
framework/framework-media-stubs-publicapi/android_common/javac/classes/\
android/media/MediaSession2.class | grep Null && echo success || echo fail

Change-Id: I60c82e0fd495d379d7107e43542b846ca50b1e96