MIDI: Flag virtual UMP

This CL flags the new virtual UMP MIDI APIs in UmpMidiDeviceService.
This CL also adds a check in MidiService to enforce the flag.

Bug: 291115176
Bug: 301713211
Test: atest MidiEchoTest
Test: adb logcat *:S MidiService:V
Change-Id: I29d12ea35a4a4231a0e67e4abcef2a149ee48ebc