WIP: Reworked Target System and Toplevel Capture

[Ferdi265]

WIP PR for implementing non-wl_output target support and toplevel capture, among other things.

Related Issues:

• Different output name format, aka make/model matching (Support for different output name format #58)
• Toplevel Capture (Support for individual window capture #61)

Current State:

• mirror/target.c generic mirror target type
  • Output Targets
    • output name matching on make/model is partially implemented (wlr output management protocol not used yet, so doesn't work on wlroots since it advertises "Unknown Unknown" for every output in wl_output)
  • Toplevel Targets
• options.c changes:
  • Refactor output and region finding code (potentially move to mirror/target.c)
• wayland.c changes:
  • Refactor output_list_node_t handling in wayland.c
  • Add toplevel list handling to wayland.c
• egl.c changes
  • Remove wl_output specific hacks

[Ferdi265]

This was an ugly refactor, wl-mirror definitely needs to be changed to be less coupled between files, and needs to make less assumptions. Hopefully once this PR is finished we'll have a better base to build future things off of.

The current state introduces the indirection layer of an opaque wlm_mirror_target_t type that is used to represent a target. The next step is to implement toplevel listing and adjust CLI parsing to actually create the correct type of target.

After initial toplevel capture works the next step is to clean up leftover hacks and fix regressions around region handling.

Finally, document the resulting design before merging.