"active source" flag handling is a weird monkeypatch

[bzbarsky]

https://webaudio.github.io/web-audio-api/#dom-audioworkletprocessor-process says:

At the conclusion of each call to the process() method, ToBoolean (described in [ECMASCRIPT]) is applied to the return value and the result is assigned to the associated AudioWorkletProcessor’s active source flag.

This is a pretty weird place to put that handling, imo, assuming this is meant to be a normative requirement (which I assume it is, since nothing else really sets the flag). It would be a lot clearer if it happened at https://webaudio.github.io/web-audio-api/#rendering-a-graph step 3.4.4.2.3 or so, where we actually make the call. Otherwise it's pretty easy to miss this requirement while implementing the processing model steps.

Having an informative note about what the function's return value means does make some sense.