References held by contained stream objects must use an internal refcount, otherwise they prevent release of the media source if Start() and Shutdown() are not called.
-- v4: winegstreamer: Release stream references to the media source in Shutdown(). winegstreamer: Do not create MF stream objects until the media source is started. mfplat/tests: Test video stream release after media source release. mfplat/tests: Add more media source refcount checks. mfplat/tests: Always free media events sent to the callback.