[worklets] Post-resolution tasks for `addModule()` call

[hoch]

In AudioWorklet, we (AudioWG) are going to have this step when the addModule() call gets resolved:

... this internal storage is populated from node name to processor definition map by extracting a node name and the matching value from parameterDescriptors when a promise from addModule() on the Worklet gets resolved.

The step should happen on the main thread, mainly to keep a "thread-specific" copy of necessary information for the construction of worklet-related objects. It is valid to have multiple WorkletGlobalScopes with AudioWorklet, so this post-resolution step is useful when synchronizing all instances of WorkletGlobalScopes and associated main thread proxy objects (e.g. BaseAudioContext).

I believe having the spec text that describes this step would be actually clear and useful. Is this something planned? If not, what's the best path to introduce this?

[joeberkovitz]

Another related approach would be to specify that all actions performed in a WorkletGlobalScope that are "queued to the main thread" are performed before the resolution of the addModule() promise (which itself can be seen as a queued task that only gets its turn after these actions complete).