types/ptr: move all the ptrTo funcs to one new package's ptr.To

Change-Id: Ia0b820ffe7aa72897515f19bd415204b6fe743c7
Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>

types/ptr/ptr.go

@@ -0,0 +1,11 @@
+// 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.
+
+// Package ptr contains the ptr.To function.
+package ptr
+
+// To returns a pointer to a shallow copy of v.
+func To[T any](v T) *T {
+	return &v
+}