Draft: wayland: Check serial for activation if no surface is provided

Having a "requester" surface helps with accuracy (e.g. ensuring the pointer is still within coordinates, besides the token serial still remaining valid). In the case we don't have one, still check the serial so that we know no other button presses/etc happened in between and activate the window if none happened.

NB: being more lenient about the requester surface perhaps help Firefox and other clients, not sure.