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/modules/fomantic/checkbox.ts

@@ -1,4 +1,4 @@
-import {linkLabelAndInput} from './base.js';
+import {linkLabelAndInput} from './base.ts';
 
 export function initAriaCheckboxPatch() {
   // link the label and the input element so it's clickable and accessible

web_src/js/modules/fomantic/dimmer.ts

@@ -1,5 +1,5 @@
 import $ from 'jquery';
-import {queryElemChildren} from '../../utils/dom.js';
+import {queryElemChildren} from '../../utils/dom.ts';
 
 export function initFomanticDimmer() {
   // stand-in for removed dimmer module

web_src/js/modules/fomantic/dropdown.ts

@@ -1,5 +1,5 @@
 import $ from 'jquery';
-import {generateAriaId} from './base.js';
+import {generateAriaId} from './base.ts';
 
 const ariaPatchKey = '_giteaAriaPatchDropdown';
 const fomanticDropdownFn = $.fn.dropdown;

web_src/js/modules/fomantic/form.ts

@@ -1,4 +1,4 @@
-import {linkLabelAndInput} from './base.js';
+import {linkLabelAndInput} from './base.ts';
 
 export function initAriaFormFieldPatch() {
   // link the label and the input element so it's clickable and accessible