Find a way to support Deno and TS with the same code base

Currently, you can use Comlink in Deno through one of the npm CDNs (unpkg, skypack etc). But it’d be nice to be able to import the source from GitHub directly. This currently doesn’t work as TypeScript enforces either no file extensions in imports or `.js` extension, while Deno requires the _actual_ file path (ending in `.ts`).