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/bootstrap.ts

@@ -0,0 +1,96 @@
+// DO NOT IMPORT window.config HERE!
+// to make sure the error handler always works, we should never import `window.config`, because
+// some user's custom template breaks it.
+
+// This sets up the URL prefix used in webpack's chunk loading.
+// This file must be imported before any lazy-loading is being attempted.
+__webpack_public_path__ = `${window.config?.assetUrlPrefix ?? '/assets'}/`;
+
+function shouldIgnoreError(err) {
+  const ignorePatterns = [
+    '/assets/js/monaco.', // https://github.com/go-gitea/gitea/issues/30861 , https://github.com/microsoft/monaco-editor/issues/4496
+  ];
+  for (const pattern of ignorePatterns) {
+    if (err.stack?.includes(pattern)) return true;
+  }
+  return false;
+}
+
+export function showGlobalErrorMessage(msg, msgType = 'error') {
+  const msgContainer = document.querySelector('.page-content') ?? document.body;
+  const msgCompact = msg.replace(/\W/g, '').trim(); // compact the message to a data attribute to avoid too many duplicated messages
+  let msgDiv = msgContainer.querySelector(`.js-global-error[data-global-error-msg-compact="${msgCompact}"]`);
+  if (!msgDiv) {
+    const el = document.createElement('div');
+    el.innerHTML = `<div class="ui container js-global-error tw-my-[--page-spacing]"><div class="ui ${msgType} message tw-text-center tw-whitespace-pre-line"></div></div>`;
+    msgDiv = el.childNodes[0];
+  }
+  // merge duplicated messages into "the message (count)" format
+  const msgCount = Number(msgDiv.getAttribute(`data-global-error-msg-count`)) + 1;
+  msgDiv.setAttribute(`data-global-error-msg-compact`, msgCompact);
+  msgDiv.setAttribute(`data-global-error-msg-count`, msgCount.toString());
+  msgDiv.querySelector('.ui.message').textContent = msg + (msgCount > 1 ? ` (${msgCount})` : '');
+  msgContainer.prepend(msgDiv);
+}
+
+/**
+ * @param {ErrorEvent|PromiseRejectionEvent} event - Event
+ * @param {string} event.message - Only present on ErrorEvent
+ * @param {string} event.error - Only present on ErrorEvent
+ * @param {string} event.type - Only present on ErrorEvent
+ * @param {string} event.filename - Only present on ErrorEvent
+ * @param {number} event.lineno - Only present on ErrorEvent
+ * @param {number} event.colno - Only present on ErrorEvent
+ * @param {string} event.reason - Only present on PromiseRejectionEvent
+ * @param {number} event.promise - Only present on PromiseRejectionEvent
+ */
+function processWindowErrorEvent({error, reason, message, type, filename, lineno, colno}) {
+  const err = error ?? reason;
+  const assetBaseUrl = String(new URL(__webpack_public_path__, window.location.origin));
+  const {runModeIsProd} = window.config ?? {};
+
+  // `error` and `reason` are not guaranteed to be errors. If the value is falsy, it is likely a
+  // non-critical event from the browser. We log them but don't show them to users. Examples:
+  // - https://developer.mozilla.org/en-US/docs/Web/API/ResizeObserver#observation_errors
+  // - https://github.com/mozilla-mobile/firefox-ios/issues/10817
+  // - https://github.com/go-gitea/gitea/issues/20240
+  if (!err) {
+    if (message) console.error(new Error(message));
+    if (runModeIsProd) return;
+  }
+
+  if (err instanceof Error) {
+    // If the error stack trace does not include the base URL of our script assets, it likely came
+    // from a browser extension or inline script. Do not show such errors in production.
+    if (!err.stack?.includes(assetBaseUrl) && runModeIsProd) return;
+    // Ignore some known errors that are unable to fix
+    if (shouldIgnoreError(err)) return;
+  }
+
+  let msg = err?.message ?? message;
+  if (lineno) msg += ` (${filename} @ ${lineno}:${colno})`;
+  const dot = msg.endsWith('.') ? '' : '.';
+  const renderedType = type === 'unhandledrejection' ? 'promise rejection' : type;
+  showGlobalErrorMessage(`JavaScript ${renderedType}: ${msg}${dot} Open browser console to see more details.`);
+}
+
+function initGlobalErrorHandler() {
+  if (window._globalHandlerErrors?._inited) {
+    showGlobalErrorMessage(`The global error handler has been initialized, do not initialize it again`);
+    return;
+  }
+  if (!window.config) {
+    showGlobalErrorMessage(`Gitea JavaScript code couldn't run correctly, please check your custom templates`);
+  }
+  // we added an event handler for window error at the very beginning of <script> of page head the
+  // handler calls `_globalHandlerErrors.push` (array method) to record all errors occur before
+  // this init then in this init, we can collect all error events and show them.
+  for (const e of window._globalHandlerErrors || []) {
+    processWindowErrorEvent(e);
+  }
+  // then, change _globalHandlerErrors to an object with push method, to process further error
+  // events directly
+  window._globalHandlerErrors = {_inited: true, push: (e) => processWindowErrorEvent(e)};
+}
+
+initGlobalErrorHandler();