Add 'shadowrealm-in-audioworklet' global
This will add to any test with global=shadowrealm in its metadata, an
.any.shadowrealm-in-audioworklet.html variant.
The wrapper here is similar to the one for ServiceWorkers, since dynamic
import() is also forbidden in worklet scopes. But additionally fetch() is
not exposed, so we add a utility function to set up the ability to call
the window realm's fetch() through the AudioWorklet's message port.
We also add /resources/testharness-shadowrealm-audioworkletprocessor.js to
contain most of the AudioWorklet setup boilerplate, so that it isn't
written inline in serve.py.
Note '.https.' needs to be added to the test path.