Add shell surface stubs
Add shell surface stubs

Add stubs for the wl_shell_surface interface.

Implement wl_shell_get_shell_surface by creating the shell surface and settings
its implementation to these stubs.

swaywm/wlroots,ascent12/wlroots,ascent12/wlroots,swaywm/wlroots,SirCmpwn/wlroots