Rewrite Icon and IconWithBadge with typescript (#24747)

app/javascript/mastodon/components/icon_with_badge.tsx

@@ -0,0 +1,20 @@
+import React from 'react';
+import { Icon } from './icon';
+
+const formatNumber = (num: number): number | string => num > 40 ? '40+' : num;
+
+type Props = {
+  id: string;
+  count: number;
+  issueBadge: boolean;
+  className: string;
+}
+const IconWithBadge: React.FC<Props> = ({ id, count, issueBadge, className }) => (
+  <i className='icon-with-badge'>
+    <Icon id={id} fixedWidth className={className} />
+    {count > 0 && <i className='icon-with-badge__badge'>{formatNumber(count)}</i>}
+    {issueBadge && <i className='icon-with-badge__issue-badge' />}
+  </i>
+);
+
+export default IconWithBadge;