wayland/surface: Add support for wl_surface.offset

This aims to replace the x,y arguments in wl_surface.attach(); meaning it can be used more sanely together with EGL, and at all when using Vulkan.

The most common use case for the offset is setting the hotspot of DND surfaces.

Marked as draft as it depends on a future libwayland release that includes https://gitlab.freedesktop.org/wayland/wayland/-/merge_requests/123