chore: Use Typescript to lint JSDoc annotations (#986)

This patch starts using typescript to lint JSDoc annotations.

Note: this uses typescript's bleeding edge. We should migrate to stable once
it has all the necessary bugfixes.

References #65.

lib/externs.d.ts

@@ -0,0 +1,28 @@
+import { Connection as RealConnection, Session as RealSession } from './Connection.js';
+import {Browser as RealBrowser, TaskQueue as RealTaskQueue} from './Browser.js';
+import * as RealPage from './Page.js';
+import {Mouse as RealMouse, Keyboard as RealKeyboard, Touchscreen as RealTouchscreen}  from './Input.js';
+import {Frame as RealFrame, FrameManager as RealFrameManager}  from './FrameManager.js';
+import {JSHandle as RealJSHandle, ExecutionContext as RealExecutionContext}  from './ExecutionContext.js';
+import * as RealElementHandle  from './ElementHandle.js';
+import * as RealNetworkManager from './NetworkManager.js';
+import * as child_process from 'child_process';
+export as namespace Puppeteer;
+
+export class Connection extends RealConnection {}
+export class Session extends RealSession {}
+export class Mouse extends RealMouse {}
+export class Keyboard extends RealKeyboard {}
+export class Touchscreen extends RealTouchscreen {}
+export class TaskQueue extends RealTaskQueue {}
+export class Browser extends RealBrowser {}
+export class Frame extends RealFrame {}
+export class FrameManager extends RealFrameManager {}
+export class NetworkManager extends RealNetworkManager {}
+export class ElementHandle extends RealElementHandle {}
+export class JSHandle extends RealJSHandle {}
+export class ExecutionContext extends RealExecutionContext {}
+export class Page extends RealPage {}
+
+
+export interface ChildProcess extends child_process.ChildProcess {}