Rename CanvasItem.update() to queue_redraw()

Affects a lot of classes. Very thoroughly checked signal connections and deferred calls to this method, add_do_method/add_undo_method calls, and so on.

Also renames the internal `_update_callback()` to `_redraw_callback()` for consistency.

Just a few comments have also been changed to say "redraw".

In CPUParticles2D, there was a private variable with the same name. It has been renamed to `do_redraw`.

scene/2d/path_2d.cpp

@@ -131,7 +131,7 @@ void Path2D::_curve_changed() {
 		return;
 	}
 
-	update();
+	queue_redraw();
 }
 
 void Path2D::set_curve(const Ref<Curve2D> &p_curve) {