Call some CanvasItem property setters only if needed

The CanvasItem property setters `set_modulate`, `set_self_modulate`
and `set_light_mask` have some side effects that don't need to be run
if the value hasn't changed.

This closes #31777.

scene/2d/canvas_item.cpp

@@ -641,6 +641,9 @@ void CanvasItem::update() {
 
 void CanvasItem::set_modulate(const Color &p_modulate) {
 
+	if (modulate == p_modulate)
+		return;
+
 	modulate = p_modulate;
 	VisualServer::get_singleton()->canvas_item_set_modulate(canvas_item, modulate);
 }
@@ -679,6 +682,9 @@ CanvasItem *CanvasItem::get_parent_item() const {
 
 void CanvasItem::set_self_modulate(const Color &p_self_modulate) {
 
+	if (self_modulate == p_self_modulate)
+		return;
+
 	self_modulate = p_self_modulate;
 	VisualServer::get_singleton()->canvas_item_set_self_modulate(canvas_item, self_modulate);
 }
@@ -689,6 +695,9 @@ Color CanvasItem::get_self_modulate() const {
 
 void CanvasItem::set_light_mask(int p_light_mask) {
 
+	if (light_mask == p_light_mask)
+		return;
+
 	light_mask = p_light_mask;
 	VS::get_singleton()->canvas_item_set_light_mask(canvas_item, p_light_mask);
 }