Change HTTPClientRequestBody.produce into ConcludingAsyncWriter.write

[guoye-zhang]

HTTPClientRequestBody.produce(into:) sounds weirdly backwards. I think it's more natural to think about writing in terms of the writer, so I'm hoping to flip it into ConcludingAsyncWriter.write as an extension.

[czechboy0]

Since these are equivalent, I don't have a strong lean, but I thought that functions that produce bytes into writers are usually that - functions that take a writer as a parameter. Rather than extensions on writer for each type that might be written.

One reason is that if many types want to write into the writer, then the Writer type itself can get many function overloads, which might get harder to use.

So I probably prefer:

extension Producer {
  func write(into writer: Writer) async throws
}

over:

extension Writer {
  func write(_ producer: Producer) async throws
}