Rework polyfills loading (#24907)

app/javascript/mastodon/polyfills/base_polyfills.ts

@@ -0,0 +1,27 @@
+import 'intl';
+import 'intl/locale-data/jsonp/en';
+import 'core-js/features/object/assign';
+import 'core-js/features/object/values';
+import 'core-js/features/symbol';
+import 'core-js/features/promise/finally';
+import { decode as decodeBase64 } from '../utils/base64';
+
+if (!HTMLCanvasElement.prototype.toBlob) {
+  const BASE64_MARKER = ';base64,';
+
+  Object.defineProperty(HTMLCanvasElement.prototype, 'toBlob', {
+    value(callback: BlobCallback, type = 'image/png', quality: any)  {
+      const dataURL = this.toDataURL(type, quality);
+      let data;
+
+      if (dataURL.indexOf(BASE64_MARKER) >= 0) {
+        const [, base64] = dataURL.split(BASE64_MARKER);
+        data = decodeBase64(base64);
+      } else {
+        [, data] = dataURL.split(',');
+      }
+
+      callback(new Blob([data], { type }));
+    },
+  });
+}