Introduce FontsContract.fetchFonts and expose URI for watching.

FontsContract.fetchFonts provides a low level font access with fonts
provider.
This CL also includes:
- Introduce new class FontFamilyResult/Font as the inner static class
of FontsContract which are used to for result value of fetchFont..
- Introduce a functionality to FontsContract to be able to create
Typeface from an array of FontResult.
- Expose URI of each file entries to be able to register ContentObserver

Bug: 36494487
Bug: 36085028
Test: android.provider.FontsContract passes
Test: android.graphics.cts.TypefaceTest passes
Test: android.graphics.fonts.cts.FontResultTest passes

Change-Id: Id6f85039d0e86be063ef099d7ec6bfd97e4424c5