rpc, p2p/simulations: use github.com/gorilla/websocket (#20289)

* rpc: improve codec abstraction

rpc.ServerCodec is an opaque interface. There was only one way to get a
codec using existing APIs: rpc.NewJSONCodec. This change exports
newCodec (as NewFuncCodec) and NewJSONCodec (as NewCodec). It also makes
all codec methods non-public to avoid showing internals in godoc.

While here, remove codec options in tests because they are not
supported anymore.

* p2p/simulations: use github.com/gorilla/websocket

This package was the last remaining user of golang.org/x/net/websocket.
Migrating to the new library wasn't straightforward because it is no
longer possible to treat WebSocket connections as a net.Conn.

* vendor: delete golang.org/x/net/websocket

* rpc: fix godoc comments and run gofmt

rpc/ipc.go

@@ -35,7 +35,7 @@ func (s *Server) ServeListener(l net.Listener) error {
 			return err
 		}
 		log.Trace("Accepted RPC connection", "conn", conn.RemoteAddr())
-		go s.ServeCodec(NewJSONCodec(conn), OptionMethodInvocation|OptionSubscriptions)
+		go s.ServeCodec(NewCodec(conn), 0)
 	}
 }
 
@@ -51,6 +51,6 @@ func DialIPC(ctx context.Context, endpoint string) (*Client, error) {
 		if err != nil {
 			return nil, err
 		}
-		return NewJSONCodec(conn), err
+		return NewCodec(conn), err
 	})
 }