xwayland: use get_pointer_device() for enter/leave handling too

In Weston, clicking the window decoration of an Xwayland client gives us a
wl_pointer.button event immediately followed by a wl_pointer.leave event.
The leave event does not contain any button state information, so the button
remains logically down in the DIX.

Once the pointer button is released, a wl_pointer.enter event is sent with
the current button state (zero). This needs to trigger a ButtonRelease event
but for that we need to ensure that the device is the same as the one we send
ButtonPress events through.

Fixes a regression introduced in a4095162.

Signed-off-by: Peter Hutterer <peter.hutterer@who-t.net>
Reviewed-by: Olivier Fourdan <ofourdan@redhat.com>
4 jobs for wip/fix-xwayland-stuck-button in 6 minutes and 51 seconds