Fix AssertionFailedError in MediaSessionCompatTest
Fix AssertionFailedError in MediaSessionCompatTest

This CL sets a MediaButtonReceiver in the test app to make
MediaSessionCompat constructor not throw IllegalArgumentException.

Bug: 34035629
Test: Tested on API < 21 devices
Change-Id: I22bcbe796bc5344fefcdd0531a62f96c60f83a11

androidx/androidx,AndroidX/androidx,AndroidX/androidx,aosp-mirror/platform_frameworks_support,aosp-mirror/platform_frameworks_support,AndroidX/androidx,aosp-mirror/platform_frameworks_support,androidx/androidx,AndroidX/androidx,androidx/androidx,aosp-mirror/platform_frameworks_support,AndroidX/androidx,AndroidX/androidx,aosp-mirror/platform_frameworks_support,androidx/androidx,androidx/androidx,androidx/androidx,AndroidX/androidx,androidx/androidx,androidx/androidx,androidx/androidx,AndroidX/androidx,AndroidX/androidx,AndroidX/androidx,androidx/androidx