Add tests ensuring the API conformance

[oleiade]

We should have some tests in place ensuring that the API the module exposes is consistent with the one defined by the specification.

Namely, we should have automated tests verifying that, when loaded, the web crypto module exposes the following to k6:

import crypto from 'k6/x/webcrypto'

// function
crypto.getRandomValues()

// function
crypto.randomUUID()

// SubtleCrypto Object with read-only properties
crypto.subtle

// function 
crypto.subtle.encrypt()

// function
crypto.subtle.decrypt()

// function
crypto.subtle.sign()

// function
crypto.subtle.verify()

// function
crypto.subtle.digest()

// function
crypto.subtle.generateKey()

// function
crypto.subtle.deriveKey()

// function
crypto.subtle.deriveBits()

// function
crypto.subtle.importKey()

// function
crypto.subtle.exportKey()

// function
crypto.subtle.wrapKey()

// function
crypto.subtle.unwrapKey()

[oleiade]

As we are implementing the official test suite, this can be closed.