LibWebSocket+RequestServer: Add a WebSocketImpl using libcurl

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.

vcpkg.json

@@ -9,7 +9,9 @@
       "name": "curl",
       "features": [
         "brotli",
-        "http2"
+        "http2",
+        "ssl",
+        "websockets"
       ]
     },
     {