xwayland: Notify of root size change with XRandR emulation
Some clients (typically Java, bu maybe others) rely on ConfigureNotify or RRScreenChangeNotify events to tell that the XRandR request is successful.
When emulated XRandR is used in Xwayland, compute the emulated root size and send the expected ConfigureNotify and RRScreenChangeNotify events with the emulated size of the root window to the asking X11 client.
Note that the root window size does not actually change, as XRandR emulation is achieved by scaling the client window using viewports in Wayland, so this event is sort of misleading.
CC: @jwrdegoede