Overwatch 2 verifies that every kernel callback that is run, lives in user32. Introduce a callback in user32 that just forwards to the other modules' callbacks.
I don't know what to call this kind of callback, I just called it "user32 callback" for now because it's going through user32 but that's not really a good name.
It also sadly necessitates a private __wine export from user32, unless someone has a better idea for how to register the callbacks with user32.
-- v3: user32: Remove NtUserDriverCallback* kernel callbacks. winex11.drv: Convert kernel callbacks to user32 callbacks. winemac.drv: Convert kernel callbacks to user32 callbacks. wineandroid.drv: Convert kernel callbacks to user32 callbacks.