revert formdata event detection

docs/resources/changelog.md

@@ -14,7 +14,6 @@ _During the beta period, these restrictions may be relaxed in the event of a mis
 - Improved RTL styles for `<sl-button-group>` [#783](https://github.com/shoelace-style/shoelace/issues/783)
 - Improved RTL styles for the toast stack [#785](https://github.com/shoelace-style/shoelace/issues/785)
 - Improved typings for translations and localized terms
-- Improved the `FormData` event polyfill to use simpler detection logic
 - Upgraded @shoelace-style/localize to 3.0
 
 ## 2.0.0-beta.75

src/internal/formdata-event-polyfill.ts

@@ -69,8 +69,26 @@ class FormDataPolyfill extends FormData {
   }
 }
 
+function supportsFormDataEvent() {
+  const form = document.createElement('form');
+  let isSupported = false;
+
+  document.body.append(form);
+
+  form.addEventListener('submit', event => {
+    new FormData(event.target as HTMLFormElement);
+    event.preventDefault();
+  });
+
+  form.addEventListener('formdata', () => (isSupported = true));
+  form.dispatchEvent(new Event('submit', { cancelable: true }));
+  form.remove();
+
+  return isSupported;
+}
+
 function polyfillFormData() {
-  if (!window.FormData || !('FormDataEvent' in window)) {
+  if (!window.FormData || supportsFormDataEvent()) {
     return;
   }