cmd/cloner,util/codegen: refactor cloner internals to allow reuse

Also run go generate again for Copyright updates.

Signed-off-by: Maisem Ali <maisem@tailscale.com>

wgengine/wgcfg/config.go

@@ -10,7 +10,7 @@ import (
 	"tailscale.com/types/key"
 )
 
-//go:generate go run tailscale.com/cmd/cloner -type=Config,Peer -output=clone.go
+//go:generate go run tailscale.com/cmd/cloner -type=Config,Peer
 
 // Config is a WireGuard configuration.
 // It only supports the set of things Tailscale uses.

wgengine/wgcfg/wgcfg_clone.go

@@ -1,9 +1,8 @@
-// Copyright (c) 2020 Tailscale Inc & AUTHORS All rights reserved.
+// Copyright (c) 2022 Tailscale Inc & AUTHORS All rights reserved.
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
 // Code generated by tailscale.com/cmd/cloner; DO NOT EDIT.
-//go:generate go run tailscale.com/cmd/cloner -type=Config,Peer -output=clone.go
 
 package wgcfg