Add vendor to improve building speed.

This also adds ability to be built in network-constrained environment.

vendor/github.com/gin-gonic/gin/internal/bytesconv/bytesconv_1.19.go

@@ -0,0 +1,26 @@
+// Copyright 2020 Gin Core Team. All rights reserved.
+// Use of this source code is governed by a MIT style
+// license that can be found in the LICENSE file.
+
+//go:build !go1.20
+
+package bytesconv
+
+import (
+	"unsafe"
+)
+
+// StringToBytes converts string to byte slice without a memory allocation.
+func StringToBytes(s string) []byte {
+	return *(*[]byte)(unsafe.Pointer(
+		&struct {
+			string
+			Cap int
+		}{s, len(s)},
+	))
+}
+
+// BytesToString converts byte slice to string without a memory allocation.
+func BytesToString(b []byte) string {
+	return *(*string)(unsafe.Pointer(&b))
+}