Use DrmOutputManager/DrmOutput

[Drakulix]

Draft / test branch for Smithay/smithay#1576.

Supersedes / Attempts to solve issues lied out in #969.

Needs more work to actually solve those issues:

• Currently this screws up the surface threads QueueState, fix in cosmic-comp or disabled the event for forced commits in initialize_output.
• DrmOutputManager Smithay/smithay#1576 needs actual format selection (though that code is currently not used?)
• DrmOutputManager Smithay/smithay#1576 needs better fallbacks (first disable planes, try again, then set the modifier to Invalid, try again, then recover if still not working)
• DrmOutputManager Smithay/smithay#1576 take care of the case where falling back from primary plane scanout to composition breaks
• DrmOutputManager Smithay/smithay#1576 add a way to lock all compositors and switch to compositing without initializing a new output
  • Use that for mode-switches
  • Use that when drm-leasing is requested