xwm: Preserve unmaximized window size at map time

This fixes a problem that can be seen with Firefox running under xwayland.
- Start it (or another client that remembers its size and maximized state),
- resize it
- maximize it
- exit it
- restart it
- unmaximize it

The size will be changed to a default size and not the previous unmaximized
size.

To fix this, save the unmaximized height and width like we do for the
fullscreen case.

Co-authored-by: Steve Pronovost <spronovo@microsoft.com>
Co-authored-by: Brenton DeGeer <brdegeer@microsoft.com>
Signed-off-by: Hideyuki Nagase <hideyukn@microsoft.com>
Signed-off-by: Steve Pronovost <spronovo@microsoft.com>
Signed-off-by: Brenton DeGeer <brdegeer@microsoft.com>
Signed-off-by: Derek Foreman <derek.foreman@collabora.com>

xwayland/window-manager.c

@@ -3035,6 +3035,8 @@ xserver_map_shell_surface(struct weston_wm_window *window,
 						       parent->surface);
 		}
 	} else if (weston_wm_window_is_maximized(window)) {
+		window->saved_width = window->width;
+		window->saved_height = window->height;
 		xwayland_interface->set_maximized(window->shsurf);
 	} else {
 		if (weston_wm_window_type_inactive(window)) {