Support non-system Font Providers

To do this, the developer must specify the set of certificate
hashes that represent the authority's app. This allows us to
verify that the authority we find is indeed the one intended
by the developer.

Bug: 35025705
Test: runtest --path frameworks/base/core/tests/coretests/src/android/provider/FontsContractTest.java
runtest --path frameworks/base/core/tests/coretests/src/android/content/res/FontResourcesParserTest.java
CTS attached to topic
Change-Id: I605f9a93bbca8705936ead08efb4a5b4fdcc4882