Migrate ringtone picking out of MediaProvider.

Some OEMs have requested the ability to customize the ringtone
picker logic, and that's already supported by the existing
"config_defaultRingtonePickerEnabled" parameter today.

This change is a clean refactoring of the AOSP ringtone picker out
of MediaProvider and into a new "SoundPicker" module, which is
consistent with how some OEMs have already defined their own
"SoundPickerPrebuilt" module.

Bug: 134542205
Test: atest --test-mapping packages/providers/MediaProvider
Change-Id: I3460b3a264859280c23e1a804b1d1bb1e99af329