Support for Cloudflare Workers for javascript_stir

[mschwarzl]

As Cloudflare Workers directly provides the crypto API https://developers.cloudflare.com/workers/runtime-apis/web-crypto/
I added an additional check in javascript_stir to use the available crypto API.

Example usage in a Worker would be:

export default {
  async fetch(request,env,context) {    
    const _sodium = await import("libsodium-wrappers");
    await _sodium.ready;
    let binkey = _sodium.from_base64(env.PUBKEY, _sodium.base64_variants.ORIGINAL)
    return new Response('Hello');
  }
};