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/common-form.ts

@@ -0,0 +1,30 @@
+import $ from 'jquery';
+import {initAreYouSure} from '../vendor/jquery.are-you-sure.ts';
+import {handleGlobalEnterQuickSubmit} from './comp/QuickSubmit.ts';
+
+export function initGlobalFormDirtyLeaveConfirm() {
+  initAreYouSure(window.jQuery);
+  // Warn users that try to leave a page after entering data into a form.
+  // Except on sign-in pages, and for forms marked as 'ignore-dirty'.
+  if (!$('.user.signin').length) {
+    $('form:not(.ignore-dirty)').areYouSure();
+  }
+}
+
+export function initGlobalEnterQuickSubmit() {
+  document.addEventListener('keydown', (e) => {
+    if (e.key !== 'Enter') return;
+    const hasCtrlOrMeta = ((e.ctrlKey || e.metaKey) && !e.altKey);
+    if (hasCtrlOrMeta && e.target.matches('textarea')) {
+      if (handleGlobalEnterQuickSubmit(e.target)) {
+        e.preventDefault();
+      }
+    } else if (e.target.matches('input') && !e.target.closest('form')) {
+      // input in a normal form could handle Enter key by default, so we only handle the input outside a form
+      // eslint-disable-next-line unicorn/no-lonely-if
+      if (handleGlobalEnterQuickSubmit(e.target)) {
+        e.preventDefault();
+      }
+    }
+  });
+}