chore(polyfill): break DOM polyfills into external file

scripts/polyfill/polyfill.dom.js

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+(function(){
+  "use strict";
+
+  if (typeof Element.prototype.matches !== 'function') {
+    Element.prototype.matches = Element.prototype.msMatchesSelector || Element.prototype.webkitMatchesSelector || function matches(selector) {
+      var element = this;
+      var elements = (element.document || element.ownerDocument).querySelectorAll(selector);
+      var index = 0;
+      while (elements[index] && elements[index] !== element) {
+        ++index;
+      }
+      return Boolean(elements[index]);
+    };
+  }
+
+
+  if (typeof Element.prototype.closest !== 'function') {
+    Element.prototype.closest = function closest(selector) {
+      var element = this;
+      while (element && element.nodeType === 1) {
+        if (element.matches(selector)) {
+          return element;
+        }
+        element = element.parentNode;
+      }
+      return null;
+    };
+  }
+
+})();

scripts/polyfill/readme.md

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+## polyfills.js
+
+Contains all polyfills needed to work on the largest range of devices. This is the default polyfill.
+
+### Targets:
+
+- Android 4.4.2 and above
+- iOS back to iOS 8
+
+### Includes:
+
+- All ES6 features
+- zone.js
+- ES7 reflection
+
+
+## polyfills.modern.js
+
+A limited of set of polyfills to work on more modern browsers. This file limits the number of ES6 polyfills which are already natively included in modern browsers.
+
+### Targets:
+
+- Android 5.0 and above
+- iOS 9 and above
+
+### Includes:
+
+- zone.js
+- ES7 reflection,
+- ES6 polyfills, except for:
+
+new regexp features,
+math features,
+symbols,
+typed arrays,
+weak maps / weak sets
+
+
+## polyfills.ng.js
+
+Only the required polyfill for Angular 2. This does not come with any ES6 polyfills. Note that all polyfill files listed here included the required polyfills for Angular 2 to work correctly.
+
+### Targets:
+
+- Android 5.0 and above
+- iOS 10 and above
+
+### Includes:
+
+- zone.js
+- ES7 reflection
+
+
+## ECMAScript 6 Compatibility
+
+To easily judge which polyfill you may need you can check this [ES6 support table](https://kangax.github.io/compat-table/es6/).