eglut_wayland: switch from wl_shell to xdg_shell

In an attempt to get !32 (closed) unstuck, here's a re-spin from me, with a few changes:

• Rebased on main
• A few trivial suggestions from @daniels was fixed
• The xdg_toplevel and zxdg_decoration_manager_v1 stuff was dropped
  • xdg_toplevel isn't really essential to unbreak things, as it only adds features.
  • zxdg_decoration_manager_v1 isn't supported on GNOME which is the DE I use, so I can't really test it.

There's a detail that's that was pointed out by @daniels in !32 (closed) that still applies to this MR, but I've reopened the discussions quoting him below.