types/persist: split controlclient.Persist into a small leaf package

This one alone doesn't modify the global dependency map much
(depaware.txt if anything looks slightly worse), but it leave
controlclient as only containing NetworkMap:

bradfitz@tsdev:~/src/tailscale.com/ipn$ grep -F "controlclient." *.go
backend.go:     NetMap        *controlclient.NetworkMap // new netmap received
fake_test.go:   b.notify(Notify{NetMap: &controlclient.NetworkMap{}})
fake_test.go:   b.notify(Notify{NetMap: &controlclient.NetworkMap{}})
handle.go:      netmapCache       *controlclient.NetworkMap
handle.go:func (h *Handle) NetMap() *controlclient.NetworkMap {

Once that goes into a leaf package, then ipn doesn't depend on
controlclient at all, and then the client gets smaller.

Updates #1278

types/persist/persist.go

@@ -0,0 +1,73 @@
+// Copyright (c) 2021 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 persist contains the Persist type.
+package persist
+
+import (
+	"fmt"
+
+	"tailscale.com/types/structs"
+	"tailscale.com/types/wgkey"
+)
+
+//go:generate go run tailscale.com/cmd/cloner -type=Persist -output=persist_clone.go
+
+// Persist is the JSON type stored on disk on nodes to remember their
+// settings between runs.
+type Persist struct {
+	_ structs.Incomparable
+
+	// LegacyFrontendPrivateMachineKey is here temporarily
+	// (starting 2020-09-28) during migration of Windows users'
+	// machine keys from frontend storage to the backend. On the
+	// first LocalBackend.Start call, the backend will initialize
+	// the real (backend-owned) machine key from the frontend's
+	// provided value (if non-zero), picking a new random one if
+	// needed. This field should be considered read-only from GUI
+	// frontends. The real value should not be written back in
+	// this field, lest the frontend persist it to disk.
+	LegacyFrontendPrivateMachineKey wgkey.Private `json:"PrivateMachineKey"`
+
+	PrivateNodeKey    wgkey.Private
+	OldPrivateNodeKey wgkey.Private // needed to request key rotation
+	Provider          string
+	LoginName         string
+}
+
+func (p *Persist) Equals(p2 *Persist) bool {
+	if p == nil && p2 == nil {
+		return true
+	}
+	if p == nil || p2 == nil {
+		return false
+	}
+
+	return p.LegacyFrontendPrivateMachineKey.Equal(p2.LegacyFrontendPrivateMachineKey) &&
+		p.PrivateNodeKey.Equal(p2.PrivateNodeKey) &&
+		p.OldPrivateNodeKey.Equal(p2.OldPrivateNodeKey) &&
+		p.Provider == p2.Provider &&
+		p.LoginName == p2.LoginName
+}
+
+func (p *Persist) Pretty() string {
+	var mk, ok, nk wgkey.Key
+	if !p.LegacyFrontendPrivateMachineKey.IsZero() {
+		mk = p.LegacyFrontendPrivateMachineKey.Public()
+	}
+	if !p.OldPrivateNodeKey.IsZero() {
+		ok = p.OldPrivateNodeKey.Public()
+	}
+	if !p.PrivateNodeKey.IsZero() {
+		nk = p.PrivateNodeKey.Public()
+	}
+	ss := func(k wgkey.Key) string {
+		if k.IsZero() {
+			return ""
+		}
+		return k.ShortString()
+	}
+	return fmt.Sprintf("Persist{lm=%v, o=%v, n=%v u=%#v}",
+		ss(mk), ss(ok), ss(nk), p.LoginName)
+}