Use @UsesReflection for FeatureFactory keep rule

Ensure FeatureFactory implementations are kept using a @UsesReflection
annotation at the callsite where they are instantiated via reflection.

Also clean up the remaining stale/unnecessary keep rules.

Bug: 272041779
Test: m + validate FeatureFactoryImpl is kept
Change-Id: I5ae3f66d8f72401568dddcac72927a87919b8afa
3 files changed