These tests are for implementing encoding of sink writer. The implements MR is !7160, working in progress. Submitted the tests MR first.
-- v3: mfreadwrite/tests: Test sample processing for mp4 sink writer. mfreadwrite/tests: Test getting transforms from mp4 sink writer. mfreadwrite/tests: Test AddStream and SetInputMediaType for mp4 sink writer. mfreadwrite/tests: Remove trivial if.