bass: Add handover related test cases

This CL adds two tests related to handover test cases. First is related
to controlling bass via LeAudioService. Second test is about controlling
bass via source stream notifications.

Tag: #feature
Test: atest LeAudioServiceTest LeAudioBroadcastServiceTest
Bug: 298080973
Bug: 308171251
Change-Id: I9e4cb5b8dbfeecc91a764446a37300563914c8b1