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/features/repo-template.js

@@ -1,51 +0,0 @@
-import $ from 'jquery';
-import {htmlEscape} from 'escape-goat';
-import {hideElem, showElem} from '../utils/dom.js';
-
-const {appSubUrl} = window.config;
-
-export function initRepoTemplateSearch() {
-  const $repoTemplate = $('#repo_template');
-  const checkTemplate = function () {
-    const $templateUnits = $('#template_units');
-    const $nonTemplate = $('#non_template');
-    if ($repoTemplate.val() !== '' && $repoTemplate.val() !== '0') {
-      showElem($templateUnits);
-      hideElem($nonTemplate);
-    } else {
-      hideElem($templateUnits);
-      showElem($nonTemplate);
-    }
-  };
-  $repoTemplate.on('change', checkTemplate);
-  checkTemplate();
-
-  const changeOwner = function () {
-    $('#repo_template_search')
-      .dropdown({
-        apiSettings: {
-          url: `${appSubUrl}/repo/search?q={query}&template=true&priority_owner_id=${$('#uid').val()}`,
-          onResponse(response) {
-            const filteredResponse = {success: true, results: []};
-            filteredResponse.results.push({
-              name: '',
-              value: '',
-            });
-            // Parse the response from the api to work with our dropdown
-            $.each(response.data, (_r, repo) => {
-              filteredResponse.results.push({
-                name: htmlEscape(repo.repository.full_name),
-                value: repo.repository.id,
-              });
-            });
-            return filteredResponse;
-          },
-          cache: false,
-        },
-
-        fullTextSearch: true,
-      });
-  };
-  $('#uid').on('change', changeOwner);
-  changeOwner();
-}