RingtoneManager: allow video ringtone URI

When checking the MIME type for the default ringtone, also
allow it to refer to video content.

Bug: 205837340
Test: see POC + atest android.media.audio.cts.RingtoneManagerTest
Merged-In: Id9b81e2db8314bc16df77d0a9221ce93143a8012
Change-Id: Iac9f27f14bae29e0fabc31e05da2357f6f4f16c7