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/webcomponents/absolute-date.test.ts

@@ -1,4 +1,4 @@
-import {toAbsoluteLocaleDate} from './absolute-date.js';
+import {toAbsoluteLocaleDate} from './absolute-date.ts';
 
 test('toAbsoluteLocaleDate', () => {
   expect(toAbsoluteLocaleDate('2024-03-15', 'en-US', {

web_src/js/webcomponents/index.js

@@ -1,5 +0,0 @@
-import './polyfills.js';
-import '@github/relative-time-element';
-import './origin-url.js';
-import './overflow-menu.js';
-import './absolute-date.js';

web_src/js/webcomponents/index.ts

@@ -0,0 +1,5 @@
+import './polyfills.ts';
+import '@github/relative-time-element';
+import './origin-url.ts';
+import './overflow-menu.ts';
+import './absolute-date.ts';

web_src/js/webcomponents/origin-url.test.ts

@@ -1,4 +1,4 @@
-import {toOriginUrl} from './origin-url.js';
+import {toOriginUrl} from './origin-url.ts';
 
 test('toOriginUrl', () => {
   const oldLocation = window.location;

web_src/js/webcomponents/overflow-menu.ts

@@ -1,6 +1,6 @@
 import {throttle} from 'throttle-debounce';
-import {createTippy} from '../modules/tippy.js';
-import {isDocumentFragmentOrElementNode} from '../utils/dom.js';
+import {createTippy} from '../modules/tippy.ts';
+import {isDocumentFragmentOrElementNode} from '../utils/dom.ts';
 import octiconKebabHorizontal from '../../../public/assets/img/svg/octicon-kebab-horizontal.svg';
 
 window.customElements.define('overflow-menu', class extends HTMLElement {