Hide public annotations unless white listed

This is to ensure that public annotations will not appear in an API
surface unless explicitly white listed.

Fixes an issue where two conscrypt annotations, Internal and ExperimentalApi
were both accidentally part of core.current.stubs.

Test: external/conscrypt/srcgen/generate_android_src.sh and check output
Change-Id: I2636aca537563edd836a0030b703a29718a00fb6
1 file changed