Script Loader: Add polyfill for window.URL, window.DOMRect.

Pending block editor revisions for WordPress 5.4 will make use of `window.URL` and `window.DOMRect`. These are not available in Internet Explorer (or pre-Chromium Edge for `DOMRect`) and must be polyfilled to avoid script errors.

The changes make use of the existing polyfill pattern, and existing `polyfill-library` dependency. The dependency is bumped to the latest version, since the previous version did not include the `DOMRect` polyfill.

Props jorgefilipecosta.
Fixes #49360.

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git-svn-id: https://core.svn.wordpress.org/trunk@47038 1a063a9b-81f0-0310-95a4-ce76da25c4cd