xfwm4-wayland: use wlr-scene API

[adlo]

I have rewritten my Wayland port of xfwm4 for the third or fourth time.

I kept adding thousands of lines of code and then scrapping it, so the
commit history was getting full of scrapped code, so I decided to reset
to master and start from scratch.

I have created a new wayland-2 branch. At some point I may rename this
branch to wayland and rename the old wayland branch to wayland-old or
something.

My compositor now uses the wlr-scene API, which handles a lot of the
low-level stuff for you, such as rendering and damage tracking, which
makes the code much simpler to write and more easily maintainable.

I have now moved the Wayland compositor code into the original xfwm4
binary, so the Wayland compositor and X11 version are now in one
binary.

You can run the Wayland compositor with the command xfwm4 --wayland

You can find the repo here:
https://github.com/adlocode/xfwm4/tree/wayland-2

Regards
adlo