StreamSinkTransformer<S, T>.fromStreamTransformer  constructor 
- StreamTransformer<
S, T> transformer 
Creates a StreamSinkTransformer that transforms events and errors
using transformer.
This is equivalent to piping all events from the outer sink through a
stream transformed by transformer and from there into the inner sink.
Implementation
const factory StreamSinkTransformer.fromStreamTransformer(
    StreamTransformer<S, T> transformer) = StreamTransformerWrapper<S, T>;