Refactor resizeImage method (#7236)

- Use URL.createObjectURL (replace from FileReader)
- Use HTMLCanvasElement.prototype.toBlob
  (replace from HTMLCanvasElement.prototype.toDataURL)
- Use Promise (replace callback interface)

app/javascript/mastodon/load_polyfills.js

@@ -12,12 +12,13 @@ function importExtraPolyfills() {
 
 function loadPolyfills() {
   const needsBasePolyfills = !(
+    Array.prototype.includes &&
+    HTMLCanvasElement.prototype.toBlob &&
     window.Intl &&
+    Number.isNaN &&
     Object.assign &&
     Object.values &&
-    Number.isNaN &&
-    window.Symbol &&
-    Array.prototype.includes
+    window.Symbol
   );
 
   // Latest version of Firefox and Safari do not have IntersectionObserver.