Fix UI not fully updating while resizing window on Windows and macOS.

This is still not fully correct, since the event loop is blocked by GHOST
and no timer events are happening for animation while the mouse is still.
But for the most part it looks ok.

source/blender/windowmanager/intern/wm_window.c

@@ -123,6 +123,7 @@ static struct WMInitStruct {
 /* ******** win open & close ************ */
 
 static void wm_window_set_drawable(wmWindowManager *wm, wmWindow *win, bool activate);
+static int wm_window_timer(const bContext *C);
 
 /* XXX this one should correctly check for apple top header...
  * done for Cocoa : returns window contents (and not frame) max size*/
@@ -1422,6 +1423,8 @@ static int ghost_event_proc(GHOST_EventHandle evt, GHOST_TUserDataPtr C_void_ptr
 
 #if defined(__APPLE__) || defined(WIN32)
 						/* OSX and Win32 don't return to the mainloop while resize */
+						wm_window_timer(C);
+						wm_event_do_handlers(C);
 						wm_event_do_notifiers(C);
 						wm_draw_update(C);