Add vendor to improve building speed.

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

vendor/golang.org/x/net/idna/go118.go

@@ -0,0 +1,13 @@
+// Code generated by running "go generate" in golang.org/x/text. DO NOT EDIT.
+
+// Copyright 2021 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+//go:build go1.18
+
+package idna
+
+// Transitional processing is disabled by default in Go 1.18.
+// https://golang.org/issue/47510
+const transitionalLookup = false