chore: rename all JS files to TS files (#6297)

core/msg.ts

@@ -0,0 +1,24 @@
+/**
+ * @license
+ * Copyright 2013 Google LLC
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+/**
+ * @fileoverview Empty name space for the Message singleton.
+ */
+'use strict';
+
+/**
+ * Empty name space for the Message singleton.
+ * @namespace Blockly.Msg
+ */
+goog.module('Blockly.Msg');
+
+
+/**
+ * A dictionary of localised messages.
+ * @type {!Object<string>}
+ */
+const Msg = Object.create(null);
+exports.Msg = Msg;