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
diff --git a/AconfigFlags.bp b/AconfigFlags.bp
index 003b7f8..abcc158 100644
--- a/AconfigFlags.bp
+++ b/AconfigFlags.bp
@@ -42,6 +42,7 @@
     ":android.credentials.flags-aconfig-java{.generated_srcjars}",
     ":android.view.contentprotection.flags-aconfig-java{.generated_srcjars}",
     ":android.service.voice.flags-aconfig-java{.generated_srcjars}",
+    ":aconfig_midi_flags_java_lib{.generated_srcjars}",
     ":android.service.autofill.flags-aconfig-java{.generated_srcjars}",
 ]