refactor: replace debounce/throttle deps with first-party code (#38610)

Adds `web_src/js/utils/func.ts` with `debounce` and `throttle`, dropping
`throttle-debounce` and `perfect-debounce` dependencies. Both were
needed before: the former has no promise-returning debounce, which
`TextExpander` requires, and the latter no `throttle`.

Signature follows lodash and es-toolkit: `(func, wait, {leading,
trailing})` plus `cancel`, so argument order flips at the migrated call
sites.

web_src/js/features/ref-issue.ts

@@ -3,7 +3,7 @@ import {GET} from '../modules/fetch.ts';
 import {createApp} from 'vue';
 import {createTippy, getAttachedTippyInstance} from '../modules/tippy.ts';
 import {addDelegatedEventListener} from '../utils/dom.ts';
-import type {Issue} from '../types.ts';
+import type {Issue, TimeoutId} from '../types.ts';
 
 type IssueInfo = {
   convertedIssue: Issue,
@@ -55,7 +55,7 @@ export function initRefIssueContextPopup() {
     link.setAttribute('data-ref-issue-popup', '');
 
     // delay so a mouse passing over the link doesn't fire a fetch
-    let timer: ReturnType<typeof setTimeout>;
+    let timer: TimeoutId;
     const cancel = () => {
       clearTimeout(timer);
       link.removeAttribute('data-ref-issue-popup');