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/ActionRunStatus.vue

@@ -2,8 +2,8 @@
     Please also update the template file above if this vue is modified.
     action status accepted: success, skipped, waiting, blocked, running, failure, cancelled, unknown
 -->
-<script>
-import {SvgIcon} from '../svg.js';
+<script lang="ts">
+import {SvgIcon} from '../svg.ts';
 
 export default {
   components: {SvgIcon},