Fetch does not support webstreams

[richarddavison]

Currently, fetch only support reading entire responses and requests from and into memory.
The streaming API's of Request and Response is not implemented.
Since the introduction of native streaming API's by @jackkleeman this functionality is now possible.
Spec is here:
https://fetch.spec.whatwg.org/#body
body should return a ReadableStream.

Currently we return null:

llrt/modules/llrt_http/src/response.rs

Line 316 in 38af490

#[qjs(get)]

[richarddavison]

Is this something you would be interested taking a look at @jackkleeman? 🥇