Allow top level metadata schemas beyond AppFunctionStaticMetadata.

This change does the following:
1. Use document ids instead of functionId to maintain a map of documents
   related to AppFunctions.
2. Rename the classes to better match their functionality.
3. Prefix all doc ids with app package name to prevent conflicts when
   same function exist in two apps.

go/appfn-additional-metadata-types-indexer

Flag: com.android.appsearch.flags.enable_app_functions_schema_parser
Test: atest AppsIndexerTests
Bug: 380729091
Change-Id: I59cb4810d6ee4532ab9aab035ce4af6d10098dc6
14 files changed