eglut_wayland, vulkan/wsi/wayland: use libdecor for top-level decoration

~~This is an RFC, and I won't mind if people object to adding this, since eglut_wayland and vulkan/wsi were using only core Wayland protocols prior to this change.

With the change, the clients will try to enable server-side decoration, and fallback to client-side decoration if the compositor does not support zxdg_decoration_v1 / requests the client to use CSD.~~

Use libdecor instead of trying to do everything by ourselves. It handles server-side decoration (SSD) directly, and nicely fallbacks to a basic client-side decoration if the compositor does not support SSD.