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/components/ScopedAccessTokenSelector.vue

@@ -1,6 +1,6 @@
-<script>
+<script lang="ts">
 import {createApp} from 'vue';
-import {hideElem, showElem} from '../utils/dom.js';
+import {hideElem, showElem} from '../utils/dom.ts';
 
 const sfc = {
   props: {