MIDI: Add test for MidiEventMultiScheduler

This CL adds a new folder in frameworks/base for MIDI tests.
This folder can act as a folder for unit tests.

A new test is added for MidiEventMultiScheduler.
com.android.internal.midi is used so this test has to be here.

Bug: 266473128
Test: atest MidiTests --rebuild-module-info
Change-Id: If0d33bd46f8c8adf3a3425888f469f942594aca9
diff --git a/tests/MidiTests/TEST_MAPPING b/tests/MidiTests/TEST_MAPPING
new file mode 100644
index 0000000..60416a8
--- /dev/null
+++ b/tests/MidiTests/TEST_MAPPING
@@ -0,0 +1,7 @@
+{
+  "presubmit": [
+    {
+      "name": "MidiTests"
+    }
+  ]
+}