Stop exposing the URL polyfill in the global scope

This moves/exposes the `URL` polyfill similarily to the existing `ReadableStream` polyfill, rather than exposing it globally, to avoid interfering with any "outside" code.
Both the `URL` and `ReadableStream` polyfills are now exposed on the `pdfjsLib` object, such that they are accessible to the viewer components.
Furthermore, the `no-restricted-globals` ESLint rule is also enabled to prevent accidental usage of the native `URL`/`ReadableStream` implementations directly in the `src/` and `web/` folders; see also https://eslint.org/docs/rules/no-restricted-globals

Addresses the remaining TODO in https://github.com/mozilla/pdf.js/projects/6

src/shared/util.js

@@ -15,6 +15,7 @@
 
 import './compatibility';
 import { ReadableStream } from './streams_polyfill';
+import { URL } from './url_polyfill';
 
 var FONT_IDENTITY_MATRIX = [0.001, 0, 0, 0.001, 0, 0];
 
@@ -1075,6 +1076,7 @@ export {
   readUint32,
   removeNullCharacters,
   ReadableStream,
+  URL,
   setVerbosityLevel,
   shadow,
   string32,