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/utils/color.test.ts

@@ -1,4 +1,4 @@
-import {contrastColor} from './color.js';
+import {contrastColor} from './color.ts';
 
 test('contrastColor', () => {
   expect(contrastColor('#d73a4a')).toBe('#fff');

web_src/js/utils/dom.test.ts

@@ -1,4 +1,4 @@
-import {createElementFromAttrs, createElementFromHTML} from './dom.js';
+import {createElementFromAttrs, createElementFromHTML} from './dom.ts';
 
 test('createElementFromHTML', () => {
   expect(createElementFromHTML('<a>foo<span>bar</span></a>').outerHTML).toEqual('<a>foo<span>bar</span></a>');

web_src/js/utils/image.test.ts

@@ -1,4 +1,4 @@
-import {pngChunks, imageInfo} from './image.js';
+import {pngChunks, imageInfo} from './image.ts';
 
 const pngNoPhys = 'data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAAEAAAABCAAAAAA6fptVAAAADUlEQVQIHQECAP3/AAAAAgABzePRKwAAAABJRU5ErkJggg==';
 const pngPhys = 'data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAAIAAAACCAIAAAD91JpzAAAACXBIWXMAABYlAAAWJQFJUiTwAAAAEElEQVQI12OQNZcAIgYIBQAL8gGxdzzM0A==';

web_src/js/utils/match.test.ts

@@ -1,4 +1,4 @@
-import {matchEmoji, matchMention} from './match.js';
+import {matchEmoji, matchMention} from './match.ts';
 
 test('matchEmoji', () => {
   expect(matchEmoji('')).toEqual([

web_src/js/utils/time.test.ts

@@ -1,4 +1,4 @@
-import {startDaysBetween} from './time.js';
+import {startDaysBetween} from './time.ts';
 
 test('startDaysBetween', () => {
   expect(startDaysBetween(new Date('2024-02-15'), new Date('2024-04-18'))).toEqual([

web_src/js/utils/time.ts

@@ -1,6 +1,6 @@
 import dayjs from 'dayjs';
 import utc from 'dayjs/plugin/utc.js';
-import {getCurrentLocale} from '../utils.js';
+import {getCurrentLocale} from '../utils.ts';
 
 dayjs.extend(utc);
 

web_src/js/utils/url.test.ts

@@ -1,4 +1,4 @@
-import {pathEscapeSegments, isUrl} from './url.js';
+import {pathEscapeSegments, isUrl} from './url.ts';
 
 test('pathEscapeSegments', () => {
   expect(pathEscapeSegments('a/b/c')).toEqual('a/b/c');