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/modules/toast.ts

@@ -0,0 +1,72 @@
+import {htmlEscape} from 'escape-goat';
+import {svg} from '../svg.ts';
+import {animateOnce, showElem} from '../utils/dom.ts';
+import Toastify from 'toastify-js'; // don't use "async import", because when network error occurs, the "async import" also fails and nothing is shown
+
+const levels = {
+  info: {
+    icon: 'octicon-check',
+    background: 'var(--color-green)',
+    duration: 2500,
+  },
+  warning: {
+    icon: 'gitea-exclamation',
+    background: 'var(--color-orange)',
+    duration: -1, // requires dismissal to hide
+  },
+  error: {
+    icon: 'gitea-exclamation',
+    background: 'var(--color-red)',
+    duration: -1, // requires dismissal to hide
+  },
+};
+
+// See https://github.com/apvarun/toastify-js#api for options
+function showToast(message, level, {gravity, position, duration, useHtmlBody, preventDuplicates = true, ...other} = {}) {
+  const body = useHtmlBody ? String(message) : htmlEscape(message);
+  const key = `${level}-${body}`;
+
+  // prevent showing duplicate toasts with same level and message, and give a visual feedback for end users
+  if (preventDuplicates) {
+    const toastEl = document.querySelector(`.toastify[data-toast-unique-key="${CSS.escape(key)}"]`);
+    if (toastEl) {
+      const toastDupNumEl = toastEl.querySelector('.toast-duplicate-number');
+      showElem(toastDupNumEl);
+      toastDupNumEl.textContent = String(Number(toastDupNumEl.textContent) + 1);
+      animateOnce(toastDupNumEl, 'pulse-1p5-200');
+      return;
+    }
+  }
+
+  const {icon, background, duration: levelDuration} = levels[level ?? 'info'];
+  const toast = Toastify({
+    text: `
+      <div class='toast-icon'>${svg(icon)}</div>
+      <div class='toast-body'><span class="toast-duplicate-number tw-hidden">1</span>${body}</div>
+      <button class='btn toast-close'>${svg('octicon-x')}</button>
+    `,
+    escapeMarkup: false,
+    gravity: gravity ?? 'top',
+    position: position ?? 'center',
+    duration: duration ?? levelDuration,
+    style: {background},
+    ...other,
+  });
+
+  toast.showToast();
+  toast.toastElement.querySelector('.toast-close').addEventListener('click', () => toast.hideToast());
+  toast.toastElement.setAttribute('data-toast-unique-key', key);
+  return toast;
+}
+
+export function showInfoToast(message, opts) {
+  return showToast(message, 'info', opts);
+}
+
+export function showWarningToast(message, opts) {
+  return showToast(message, 'warning', opts);
+}
+
+export function showErrorToast(message, opts) {
+  return showToast(message, 'error', opts);
+}