Let IndexableProcessor support different packages

Add a new annotation option key:
com.android.settingslib.search.processor.package

So the generated SearchIndexableResources* could be in given package.

Also clean up common.mk since it's no longer used.

Bug: 284799832
Test: m Settings
Test: Manually try Settings Search
Change-Id: I5848e6fcedf4e40804c347a2f7717dc6d5f615de