Fix Windowfocus on resizing

When resizing a non-focused window, the previously focused
Window got resized.
This patch grabs focus for the actually resized window, before
starting with the resizing.

scene/main/viewport.cpp

@@ -2662,6 +2662,11 @@ bool Viewport::_sub_windows_forward_input(const Ref<InputEvent> &p_event) {
 				} else {
 					gui.subwindow_resize_mode = _sub_window_get_resize_margin(sw.window, mb->get_position());
 					if (gui.subwindow_resize_mode != SUB_WINDOW_RESIZE_DISABLED) {
+						if (gui.subwindow_focused != sw.window) {
+							// Refocus.
+							_sub_window_grab_focus(sw.window);
+						}
+
 						gui.subwindow_resize_from_rect = r;
 						gui.subwindow_drag_from = mb->get_position();
 						gui.subwindow_drag = SUB_WINDOW_DRAG_RESIZE;