Rewrote AudioDriverJavaScript to support multiple processor nodes.
The old (and deprecated) ScriptProcessorNode when threads are not
available, and the new AudioWorklet API when threads are enabled.
The new implementation uses two ring buffers and a shared state to
communicated with the AudioWorklet thread.
The audio.worklet.js JavaScript file is always added to the export
template, but only really used (and download) in the thread build.
