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/RepoActivityTopAuthors.vue

@@ -1,4 +1,4 @@
-<script>
+<script lang="ts">
 import VueBarGraph from 'vue-bar-graph';
 import {createApp} from 'vue';