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-page.ts

@@ -0,0 +1,93 @@
+import $ from 'jquery';
+import {GET} from '../modules/fetch.ts';
+import {showGlobalErrorMessage} from '../bootstrap.ts';
+
+const {appUrl} = window.config;
+
+export function initHeadNavbarContentToggle() {
+  const navbar = document.querySelector('#navbar');
+  const btn = document.querySelector('#navbar-expand-toggle');
+  if (!navbar || !btn) return;
+
+  btn.addEventListener('click', () => {
+    const isExpanded = btn.classList.contains('active');
+    navbar.classList.toggle('navbar-menu-open', !isExpanded);
+    btn.classList.toggle('active', !isExpanded);
+  });
+}
+
+export function initFootLanguageMenu() {
+  async function linkLanguageAction() {
+    const $this = $(this);
+    await GET($this.data('url'));
+    window.location.reload();
+  }
+
+  $('.language-menu a[lang]').on('click', linkLanguageAction);
+}
+
+export function initGlobalDropdown() {
+  // Semantic UI modules.
+  const $uiDropdowns = $('.ui.dropdown');
+
+  // do not init "custom" dropdowns, "custom" dropdowns are managed by their own code.
+  $uiDropdowns.filter(':not(.custom)').dropdown();
+
+  // The "jump" means this dropdown is mainly used for "menu" purpose,
+  // clicking an item will jump to somewhere else or trigger an action/function.
+  // When a dropdown is used for non-refresh actions with tippy,
+  // it must have this "jump" class to hide the tippy when dropdown is closed.
+  $uiDropdowns.filter('.jump').dropdown({
+    action: 'hide',
+    onShow() {
+      // hide associated tooltip while dropdown is open
+      this._tippy?.hide();
+      this._tippy?.disable();
+    },
+    onHide() {
+      this._tippy?.enable();
+
+      // hide all tippy elements of items after a while. eg: use Enter to click "Copy Link" in the Issue Context Menu
+      setTimeout(() => {
+        const $dropdown = $(this);
+        if ($dropdown.dropdown('is hidden')) {
+          $(this).find('.menu > .item').each((_, item) => {
+            item._tippy?.hide();
+          });
+        }
+      }, 2000);
+    },
+  });
+
+  // Special popup-directions, prevent Fomantic from guessing the popup direction.
+  // With default "direction: auto", if the viewport height is small, Fomantic would show the popup upward,
+  //   if the dropdown is at the beginning of the page, then the top part would be clipped by the window view.
+  //   eg: Issue List "Sort" dropdown
+  // But we can not set "direction: downward" for all dropdowns, because there is a bug in dropdown menu positioning when calculating the "left" position,
+  //   which would make some dropdown popups slightly shift out of the right viewport edge in some cases.
+  //   eg: the "Create New Repo" menu on the navbar.
+  $uiDropdowns.filter('.upward').dropdown('setting', 'direction', 'upward');
+  $uiDropdowns.filter('.downward').dropdown('setting', 'direction', 'downward');
+}
+
+export function initGlobalTabularMenu() {
+  $('.ui.menu.tabular:not(.custom) .item').tab({autoTabActivation: false});
+}
+
+/**
+ * Too many users set their ROOT_URL to wrong value, and it causes a lot of problems:
+ *   * Cross-origin API request without correct cookie
+ *   * Incorrect href in <a>
+ *   * ...
+ * So we check whether current URL starts with AppUrl(ROOT_URL).
+ * If they don't match, show a warning to users.
+ */
+export function checkAppUrl() {
+  const curUrl = window.location.href;
+  // some users visit "https://domain/gitea" while appUrl is "https://domain/gitea/", there should be no warning
+  if (curUrl.startsWith(appUrl) || `${curUrl}/` === appUrl) {
+    return;
+  }
+  showGlobalErrorMessage(`Your ROOT_URL in app.ini is "${appUrl}", it's unlikely matching the site you are visiting.
+Mismatched ROOT_URL config causes wrong URL links for web UI/mail content/webhook notification/OAuth2 sign-in.`, 'warning');
+}