Add direct support for running in Audio Worklet (via `-sENVIRONMENT=worklet`)

[sbc100]

There are some use cases where its useful to be able to run emscripten generated code in an audio worklet without building with -sAUDIO_WORKLET. One major example would be deploying in a context where shared memory not available (i.e. no cross origin isolation)

See #22979

[sbc100]

CC @lindell @juj @kripken

[lindell]

This is how you set up Emscripten to run in AudioWorklets when you do not have cross origin isolation:

• Get the Emscripten loader js code, and the code to manually set up the AudioWorkletProcessor and add both to the AudioWorklet conext (addModule)
• Get the .wasm url and stream-compile it into a WebAssemply.Module.
• Start the AudioWorkletNode and add the WebAssemply.Module reference to the processorOptions (can also be posted via MessageChannel).
• Use the Module.instantiateWasm field and resolve to the WebAssemply.Module provided in processorOptions
• Call into the module yourself for each process() callback.

This currently works with web,shell environment with some workarounds (see #22979). But having a dedicated environment that assumes the unique restrictions of Worklets would be great.

[sbc100]

Hopefully #25942 will solve your issue and you can just use -sENVIRONMENT=worklet. Does that PR look reasonable to you?