Add SystemFeaturesMetadataPerfTest

Add a basic perf test for querying system feature indices. Introduce
a proxy helper method for accessing this, as the method is generated
via an annotation processor with internal visibility.

Bug: 203143243
Test: atest \
    CorePerfTests:android.content.pm.SystemFeaturesMetadataPerfTest
Flag: EXEMPT Not yet used
Change-Id: I67175af22b06567bab1bdfcd7a9b148ceb1bed6e