Add TypeScript boilerplate

[marklundin]

This PR adds support for generating TS boilerplate in the createScript() method. The boilerplate is an extension of the .mjs with type annotations.

import { Script } from 'playcanvas';

/**
 * The {@link https://api.playcanvas.com/classes/Engine.Script.html | Script} class is
 * the base class for all PlayCanvas scripts. Learn more about writing scripts in the
 * {@link https://developer.playcanvas.com/user-manual/scripting/ | scripting guide}.
 */
export class MyClass extends Script {
    /**
     * Called when the script is about to run for the first time.
     */
    initialize(): void {
    }

    /**
     * Called for enabled (running state) scripts on each tick.
     * 
     * @param {number} dt - The delta time in seconds since the last frame.
     */
    update(dt: number): void {
    }
}