added mover constructor

src/core/String.cpp

@@ -73,6 +73,11 @@ String::String(const String &other) {
 	godot::api->godot_string_new_copy(&_godot_string, &other._godot_string);
 }
 
+String::String(String&& other) {
+    godot::api->godot_string_new_copy(&_godot_string, &other._godot_string);
+    godot::api->godot_string_destroy(&_godot_string);
+}
+
 String::~String() {
 	godot::api->godot_string_destroy(&_godot_string);
 }