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
61105d0618
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/modules/worker.ts

@@ -0,0 +1,9 @@
+import {sleep} from '../utils.ts';
+
+const {appSubUrl} = window.config;
+
+export async function logoutFromWorker() {
+  // wait for a while because other requests (eg: logout) may be in the flight
+  await sleep(5000);
+  window.location.href = `${appSubUrl}/`;
+}