The end goal here is for LibHTTP to be the home of our RFC 9111 (HTTP
caching) implementation. We currently have one implementation in LibWeb
for our in-memory cache and another in RequestServer for our disk cache.
The implementations both largely revolve around interacting with HTTP
headers. But in LibWeb, we are using Fetch's header infra, and in RS we
are using are home-grown header infra from LibHTTP.
So to give these a common denominator, this patch replaces the LibHTTP
implementation with Fetch's infra. Our existing LibHTTP implementation
was not particularly compliant with any spec, so this at least gives us
a standards-based common implementation.
This migration also required moving a handful of other Fetch AOs over
to LibHTTP. (It turns out these AOs were all from the Fetch/Infra/HTTP
folder, so perhaps it makes sense for LibHTTP to be the implementation
of that entire set of facilities.)
`curl_easy_recv` must be called in a loop until it returns EAGAIN,
because it may cache data, but only activate the read notifier once.
Additionally, the data received can contain multiple WebSocket frames
and only activate the notifier once, so we have to keep reading frames
until there isn't enough data.
We also have to do this immediately after connecting a WebSocket,
since the server may immediately send data when the WebSocket opens
and before we create the read notifier.
This makes Discord login faster and more reliable, and makes Discord
activities start loading.
This implementation can be better improved in the future by ripping
out a lot of the manual logic in LibWebSocket and rely on libcurl to
parse our message payloads. But for now, this uses the 'raw mode' of
curl websockets in connect-only mode to allow for somewhat seamless
integration into our event loop.
The previous implementation would call send a half-dozen times
when sending each frame of WebSocket data. This is excessive,
especially since we need to allocate a new buffer for the payload
in order to mask it anyway. Let's just allocate one buffer up front,
and send all the completed data at the end of the method
