feat: Support VLESS XTLS Vision (#406)

transport/vless/xtls.go

@@ -2,6 +2,7 @@ package vless
 
 import (
 	"context"
+	"errors"
 	"net"
 
 	tlsC "github.com/Dreamacro/clash/component/tls"
@@ -9,6 +10,10 @@ import (
 	xtls "github.com/xtls/go"
 )
 
+var (
+	ErrNotTLS13 = errors.New("XTLS Vision based on TLS 1.3 outer connection")
+)
+
 type XTLSConfig struct {
 	Host           string
 	SkipCertVerify bool