Web Streams cleanup (#56819)
This updates some code related to web streams and encoding.
- Removes some unused code related to base64 encoding/decoding (Edge runtime currently supports it natively via `Buffer`)
- Prefer readable stream `pull` versus `.on("data", (chunk) => { ... })` event handlers (simplifies execution)
- Utilize `pipeTo` and `pipeThrough` on web streams to remove custom code related to stream pumping
- Updates pipe readable function to utilize web streams first class rather than relying on manual pumping + stream management
- This also takes advantage of the `AbortController` when piping so that the response can use it to cancel the stream
