Allow Font providers to return status codes

This was requested by the current users, need to state
that a font is unavailable (needs downloading) or that
the query is unsupported.

Also add tests :)

Test: runtest --path frameworks/base/core/tests/coretests/src/android/provider/FontsContractTest.java
Also CTS attached to topic
Bug: 35097775
Change-Id: Ib15bf4c70185d81a4c20426722eb44c4210771c2