Convert frontend code to typescript (#31559)

None of the frontend js/ts files was touched besides these two commands
(edit: no longer true, I touched one file in
https://github.com/go-gitea/gitea/pull/31559/commits/61105d0618e285d97e95044bfb64415f364a4526
because of a deprecation that was not showing before the rename).

`tsc` currently reports 778 errors, so I have disabled it in CI as
planned.

Everything appears to work fine.

web_src/js/features/user-auth.ts

@@ -0,0 +1,22 @@
+import {checkAppUrl} from './common-page.ts';
+
+export function initUserAuthOauth2() {
+  const outer = document.querySelector('#oauth2-login-navigator');
+  if (!outer) return;
+  const inner = document.querySelector('#oauth2-login-navigator-inner');
+
+  checkAppUrl();
+
+  for (const link of outer.querySelectorAll('.oauth-login-link')) {
+    link.addEventListener('click', () => {
+      inner.classList.add('tw-invisible');
+      outer.classList.add('is-loading');
+      setTimeout(() => {
+        // recover previous content to let user try again
+        // usually redirection will be performed before this action
+        outer.classList.remove('is-loading');
+        inner.classList.remove('tw-invisible');
+      }, 5000);
+    });
+  }
+}