Fix some ninja variable issues in the aapt2 rules. These were
caught by app_test.go, but that wasn't being run automatically,
so add it to testSrcs.
Test: app_test.go
Change-Id: Ia01dda45ba5ced9c304056939c0e69f170c15de3
Use aapt2 instead of aapt to compile Android app resources.
Also generate all files into srcjars instead of individual
sources.
Test: m checkbuild
Change-Id: I5a67991a0daf0017e8159b46fcff7d5564a91468