v2: Handle MEError/MF_E_SHUTDOWN events on the media sources, remove additional unnecessary session interface.
I'm not opposed to such notification interface in general, but we need to figure out this undocumented API first, if it exists at all.
Fwiw I have investigated this a bit, and the session and the media source use an undocumented interface to communicate. I don't have a definitive confirmation that it's used for shutdown, but the session requests an internal `0b5e1c7e-bd76-46bc-896c-b2edb40dd803` source interface when topology is loaded.
That interface seem to extend `IUnknown` with 3 methods but some other internal objects are then involved, some of which with a large number of methods. So it doesn't seem useful to try reverse engineering this for the only purpose of notifying of shutdown, if that's the actual purpose of this (I suspect it has a wider purpose and I could not find any other obvious notification mechanism).