util/deephash: add debug printer (#5460)

When built with "deephash_debug", print the set of HashXXX methods.

Example usage:

	$ go test -run=GetTypeHasher/string_slice -tags=deephash_debug
	U64(2)+U64(3)+S("foo")+U64(3)+S("bar")+FIN

Signed-off-by: Joe Tsai <joetsai@digital-static.net>

util/deephash/debug.go

@@ -0,0 +1,38 @@
+// 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.
+
+//go:build deephash_debug
+
+package deephash
+
+import "fmt"
+
+func (h *hasher) HashBytes(b []byte) {
+	fmt.Printf("B(%q)+", b)
+	h.Block512.HashBytes(b)
+}
+func (h *hasher) HashString(s string) {
+	fmt.Printf("S(%q)+", s)
+	h.Block512.HashString(s)
+}
+func (h *hasher) HashUint8(n uint8) {
+	fmt.Printf("U8(%d)+", n)
+	h.Block512.HashUint8(n)
+}
+func (h *hasher) HashUint16(n uint16) {
+	fmt.Printf("U16(%d)+", n)
+	h.Block512.HashUint16(n)
+}
+func (h *hasher) HashUint32(n uint32) {
+	fmt.Printf("U32(%d)+", n)
+	h.Block512.HashUint32(n)
+}
+func (h *hasher) HashUint64(n uint64) {
+	fmt.Printf("U64(%d)+", n)
+	h.Block512.HashUint64(n)
+}
+func (h *hasher) Sum(b []byte) []byte {
+	fmt.Println("FIN")
+	return h.Block512.Sum(b)
+}