Allow for a streaming response

[rylev]

Fixes #981

This allows operations to expose a streaming response body so that they don't have to collect response bodies into a Bytes collection. For example, get_blob now returns back a ResponseBody as part of its response type. This type implements Stream for users who want to stream the data as well as collect methods for users that just want the data as Bytes or even as a String.

This also makes PinnedStream and collect_pinned_stream private which were always a bit of an awkward API.

This is what fetching a blob now looks like:

let mut result: Vec<u8> = vec![];
let mut stream = blob_client
     .get()
     .chunk_size(0xFFFF_FFFF_FFFFu64)
     .into_stream();
while let Some(response) = stream.next().await {
     let mut body = response?.data;
     while let Some(value) = body.next().await {
         // Instead of this while loop the user can also call `body.collect()` to get back `Bytes`
         // or `body.collect_string()` to get a `String`
         let value = value?;
         result.extend(&value);
     }
}

[cataggar]

Sorry, #984 caused some conflicts. Probably best to revert 96c66c1, merge main, and rerun codegen.

[cataggar]

This looks great!

[yoshuawuyts]

This looks really good!

[rajasekarv]

Didn't expect it to be done this quick. Thanks a lot @rylev