xwayland: Expose configure request mask

Without this information, compositors have no way to tell whether
or not to consider the position information valid. Most notably,
a compositor needs to know if it should pick a position for the
surface or use the position sent in the configure request.

include/wlr/xwayland.h

@@ -179,6 +179,7 @@ struct wlr_xwayland_surface_configure_event {
 	struct wlr_xwayland_surface *surface;
 	int16_t x, y;
 	uint16_t width, height;
+	uint16_t mask; // xcb_config_window_t
 };
 
 // TODO: maybe add a seat to these

xwayland/xwm.c

@@ -871,6 +871,7 @@ static void xwm_handle_configure_request(struct wlr_xwm *xwm,
 		.y = mask & XCB_CONFIG_WINDOW_Y ? ev->y : surface->y,
 		.width = mask & XCB_CONFIG_WINDOW_WIDTH ? ev->width : surface->width,
 		.height = mask & XCB_CONFIG_WINDOW_HEIGHT ? ev->height : surface->height,
+		.mask = mask,
 	};
 	wlr_log(WLR_DEBUG, "XCB_CONFIGURE_REQUEST (%u) [%ux%u+%d,%d]", ev->window,
 		wlr_event.width, wlr_event.height, wlr_event.x, wlr_event.y);