wl-mirror attempts to provide a solution to sway's lack of output
mirroring by mirroring an output onto a client surface.

Features:
- Mirror an output onto a resizable window
- Mirror an output onto another output by fullscreening the window
- Reacts to changes in output scale
- Preserves aspect ratio
- Corrects for flipped or rotated outputs
- Supports custom flips or rotations
- Supports mirroring custom regions of outputs
- Supports receiving additional options on stdin for changing the mirrored
  screen or region on the fly (works best when used with pipectl)