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-release.ts

@@ -0,0 +1,58 @@
+import {hideElem, showElem} from '../utils/dom.ts';
+import {initComboMarkdownEditor} from './comp/ComboMarkdownEditor.ts';
+
+export function initRepoRelease() {
+  document.addEventListener('click', (e) => {
+    if (e.target.matches('.remove-rel-attach')) {
+      const uuid = e.target.getAttribute('data-uuid');
+      const id = e.target.getAttribute('data-id');
+      document.querySelector(`input[name='attachment-del-${uuid}']`).value = 'true';
+      hideElem(`#attachment-${id}`);
+    }
+  });
+}
+
+export function initRepoReleaseNew() {
+  if (!document.querySelector('.repository.new.release')) return;
+
+  initTagNameEditor();
+  initRepoReleaseEditor();
+}
+
+function initTagNameEditor() {
+  const el = document.querySelector('#tag-name-editor');
+  if (!el) return;
+
+  const existingTags = JSON.parse(el.getAttribute('data-existing-tags'));
+  if (!Array.isArray(existingTags)) return;
+
+  const defaultTagHelperText = el.getAttribute('data-tag-helper');
+  const newTagHelperText = el.getAttribute('data-tag-helper-new');
+  const existingTagHelperText = el.getAttribute('data-tag-helper-existing');
+
+  const tagNameInput = document.querySelector('#tag-name');
+  const hideTargetInput = function(tagNameInput) {
+    const value = tagNameInput.value;
+    const tagHelper = document.querySelector('#tag-helper');
+    if (existingTags.includes(value)) {
+      // If the tag already exists, hide the target branch selector.
+      hideElem('#tag-target-selector');
+      tagHelper.textContent = existingTagHelperText;
+    } else {
+      showElem('#tag-target-selector');
+      tagHelper.textContent = value ? newTagHelperText : defaultTagHelperText;
+    }
+  };
+  hideTargetInput(tagNameInput); // update on page load because the input may have a value
+  tagNameInput.addEventListener('input', (e) => {
+    hideTargetInput(e.target);
+  });
+}
+
+function initRepoReleaseEditor() {
+  const editor = document.querySelector('.repository.new.release .combo-markdown-editor');
+  if (!editor) {
+    return;
+  }
+  initComboMarkdownEditor(editor);
+}