refact: Migrate $helper.keyboard to TypeScript (#7984)

Author: distantnative

panel/lab/internals/helpers/keyboard/index.php

@@ -1,5 +1,5 @@
 <?php
 
 return [
-	'source' => 'panel/src/helpers/keyboard.js'
+	'source' => 'panel/src/helpers/keyboard.ts'
 ];

panel/src/helpers/keyboard.js panel/src/helpers/keyboard.tspanel/src/helpers/keyboard.js renamed to panel/src/helpers/keyboard.ts

@@ -1,8 +1,7 @@
 /**
- * Returns name of meta key for current OS
- * @returns {string} `cmd` or `ctrl`
+ * Returns name of meta key for current OS (`cmd` or `ctrl`)
  */
-export function metaKey() {
+export function metaKey(): string {
 	return window.navigator.userAgent.indexOf("Mac") > -1 ? "cmd" : "ctrl";
 }