Issues with anvil's `cursor_position_hint`

[ids1024]

As mentioned in https://github.com/Smithay/smithay/pull/1551#issuecomment-2378377955, Blender seems to work well for testing this.

• With multiple monitors, pointer is warped to the first monitor; the output geometry presumably needs to be added
• The position still doesn't seem to be correct
• It looks like the implementation will ignore the hint if the WlSurface is a subsurface and not the toplevel. But I guess nothing in zwp_pointer_constraints_v1 says the surface the pointer is confined to can't be a subsurface?

Trying to implement this for cosmic-comp, I'm not sure how to get the absolute position for an arbitrary WlSurface, taking into account server-side decorations and subsurfaces....