[Proposal] Make able to write React in Typescript (#16210)

Co-authored-by: berlysia <berlysia@gmail.com>
Co-authored-by: fusagiko / takayamaki <takayamaki@users.noreply.github.com>

app/javascript/mastodon/uuid.ts

@@ -0,0 +1,3 @@
+export default function uuid(a?: string): string {
+  return a ? ((a as any as number) ^ Math.random() * 16 >> (a as any as number) / 4).toString(16) : ('' + 1e7 + -1e3 + -4e3 + -8e3 + -1e11).replace(/[018]/g, uuid);
+}