Make tooltips appear on the same display as the editor

The `current_screen` field was never being set on tooptip windows, leading to scenarios where, if the editor wasn't on screen 0, tooltips may not appear in the right place, especially when your screens have different resolutions.

scene/main/viewport.cpp

@@ -1580,7 +1580,8 @@ void Viewport::_gui_show_tooltip() {
 	Point2 tooltip_offset = ProjectSettings::get_singleton()->get("display/mouse_cursor/tooltip_position_offset");
 	Rect2 r(gui.tooltip_pos + tooltip_offset, gui.tooltip_popup->get_contents_minimum_size());
 
-	Rect2i vr = gui.tooltip_popup->get_usable_parent_rect();
+	Window *window = gui.tooltip_popup->get_parent_visible_window();
+	Rect2i vr = window->get_usable_parent_rect();
 
 	if (r.size.x + r.position.x > vr.size.x + vr.position.x) {
 		r.position.x = vr.position.x + vr.size.x - r.size.x;
@@ -1594,6 +1595,7 @@ void Viewport::_gui_show_tooltip() {
 		r.position.y = vr.position.y;
 	}
 
+	gui.tooltip_popup->set_current_screen(window->get_current_screen());
 	gui.tooltip_popup->set_position(r.position);
 	gui.tooltip_popup->set_size(r.size);