Explicitly throw an exception for unknown tags when parsing XML.

This situation shouldn't arise because compiler to generate XML and XSD
defined in SDK should always be in sync.

Test: AppsIndexerTests
Flag: com.android.appsearch.flags.enable_app_functions_schema_parser
Bug: 410519921
Change-Id: If76e372cbc4f1f7fa4509a09233786aca315b706
2 files changed