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/match.test.js

@@ -1,50 +0,0 @@
-import {matchEmoji, matchMention} from './match.js';
-
-test('matchEmoji', () => {
-  expect(matchEmoji('')).toEqual([
-    '+1',
-    '-1',
-    '100',
-    '1234',
-    '1st_place_medal',
-    '2nd_place_medal',
-  ]);
-
-  expect(matchEmoji('hea')).toEqual([
-    'headphones',
-    'headstone',
-    'health_worker',
-    'hear_no_evil',
-    'heard_mcdonald_islands',
-    'heart',
-  ]);
-
-  expect(matchEmoji('hear')).toEqual([
-    'hear_no_evil',
-    'heard_mcdonald_islands',
-    'heart',
-    'heart_decoration',
-    'heart_eyes',
-    'heart_eyes_cat',
-  ]);
-
-  expect(matchEmoji('poo')).toEqual([
-    'poodle',
-    'hankey',
-    'spoon',
-    'bowl_with_spoon',
-  ]);
-
-  expect(matchEmoji('1st_')).toEqual([
-    '1st_place_medal',
-  ]);
-
-  expect(matchEmoji('jellyfis')).toEqual([
-    'jellyfish',
-  ]);
-});
-
-test('matchMention', () => {
-  expect(matchMention('')).toEqual(window.config.mentionValues.slice(0, 6));
-  expect(matchMention('user4')).toEqual([window.config.mentionValues[3]]);
-});