feat(page): introduce page.setDefaultTimeout (#3854)

Method `page.setDefaultTimeout` overrides default 30 seconds timeout
for all `page.waitFor*` methods, including navigation and waiting
for selectors.

Fix #3319.

lib/externs.d.ts

@@ -7,6 +7,7 @@ import {Mouse as RealMouse, Keyboard as RealKeyboard, Touchscreen as RealTouchsc
 import {Frame as RealFrame, FrameManager as RealFrameManager}  from './FrameManager.js';
 import {JSHandle as RealJSHandle, ElementHandle as RealElementHandle}  from './JSHandle.js';
 import {DOMWorld as RealDOMWorld}  from './DOMWorld.js';
+import {TimeoutSettings as RealTimeoutSettings}  from './TimeoutSettings.js';
 import {ExecutionContext as RealExecutionContext}  from './ExecutionContext.js';
 import { NetworkManager as RealNetworkManager, Request as RealRequest, Response as RealResponse } from './NetworkManager.js';
 import * as child_process from 'child_process';
@@ -30,6 +31,7 @@ declare global {
     export class ElementHandle extends RealElementHandle {}
     export class JSHandle extends RealJSHandle {}
     export class DOMWorld extends RealDOMWorld {}
+    export class TimeoutSettings extends RealTimeoutSettings {}
     export class ExecutionContext extends RealExecutionContext {}
     export class Page extends RealPage { }
     export class Response extends RealResponse { }