breakup {Cts,Mcts}MediaTranscodingTestCases
separate into module/framework;
proper default exclude-annotation in respective AndroidTest*xml files
ensure that neither is empty through addition of stubs
Bug: 331566031
Flag: TEST_ONLY
Test: atest CtsMediaTranscodingTestCases
Test: atest MctsMediaTranscodingTestCases
Change-Id: Idc92a1657f809d891a9d45372eebf48855840362