Correctly insert platformBuildVersionCode/Name

AAPT(1) encodes platformBuildVersionCode and
platformBuildVersionName into the manifest along with
compileSdkVersion and compileSdkVersionCodename. AAPT2 was extracting
the platform attributes from the app being created rather than the
framework.

This change inserts the correct platform attributes.

Bug: 124227171
Test: aapt2_tests
Change-Id: I4bc7986d25f065cecf01b9e988de4d37283ef7de