by default utilises the color space of the screen on which the window is
located. if a specific value is defined, it will instead be utilised.
depending on the chosen color space the macOS EDR (HDR) support is
activated and that OS's transformation (tone mapping) is used.
Fixes#7341
add new app_bridge objc file for bridging between mpv core and app
functionality. replace old EventsResponder singleton with AppHub.
another step to clean up all App functionality and have one central
place for it.