Fix Theme type group naming in the inspector

(cherry picked from commit 197be78bc558aa90413bd0420c24736a989e5f0e)

scene/resources/theme.cpp

@@ -179,7 +179,15 @@ void Theme::_get_property_list(List<PropertyInfo> *p_list) const {
 	}
 
 	list.sort();
+	String prev_type;
 	for (List<PropertyInfo>::Element *E = list.front(); E; E = E->next()) {
+		// Add groups for types so that their names are left unchanged in the inspector.
+		String current_type = E->get().name.get_slice("/", 0);
+		if (prev_type != current_type) {
+			p_list->push_back(PropertyInfo(Variant::NIL, current_type, PROPERTY_HINT_NONE, current_type + "/", PROPERTY_USAGE_GROUP));
+			prev_type = current_type;
+		}
+
 		p_list->push_back(E->get());
 	}
 }