refactor: move various duties from ChannelRouter to graph.Builder

This commit is a large refactor that moves over various responsibilities
from the ChannelRouter to the graph.Builder. These include all graph
related tasks such as:
- graph pruning
- validation of new network updates & persisting new updates
- notifying topology update clients of any changes.

This is a large commit but:
- many of the files are purely moved from `routing` to `graph`
- the business logic put in the graph Builder is copied exactly as is
  from the ChannelRouter with one exception:
- The ChannelRouter just needs to be able to call the Builder's
  `ApplyChannelUpdate` method. So this is now exported and provided to
the ChannelRouter as a config option.
- The trickiest part was just moving over the test code since quite a
  bit had to be duplicated.

funding/manager.go

@@ -23,6 +23,7 @@ import (
 	"github.com/lightningnetwork/lnd/channeldb"
 	"github.com/lightningnetwork/lnd/channeldb/models"
 	"github.com/lightningnetwork/lnd/discovery"
+	"github.com/lightningnetwork/lnd/graph"
 	"github.com/lightningnetwork/lnd/input"
 	"github.com/lightningnetwork/lnd/keychain"
 	"github.com/lightningnetwork/lnd/labels"
@@ -33,7 +34,6 @@ import (
 	"github.com/lightningnetwork/lnd/lnwallet/chainfee"
 	"github.com/lightningnetwork/lnd/lnwallet/chanfunding"
 	"github.com/lightningnetwork/lnd/lnwire"
-	"github.com/lightningnetwork/lnd/routing"
 	"golang.org/x/crypto/salsa20"
 )
 
@@ -3415,10 +3415,10 @@ func (f *Manager) addToRouterGraph(completeChan *channeldb.OpenChannel,
 	select {
 	case err := <-errChan:
 		if err != nil {
-			if routing.IsError(err, routing.ErrOutdated,
-				routing.ErrIgnored) {
+			if graph.IsError(err, graph.ErrOutdated,
+				graph.ErrIgnored) {
 
-				log.Debugf("Router rejected "+
+				log.Debugf("Graph rejected "+
 					"ChannelAnnouncement: %v", err)
 			} else {
 				return fmt.Errorf("error sending channel "+
@@ -3435,10 +3435,10 @@ func (f *Manager) addToRouterGraph(completeChan *channeldb.OpenChannel,
 	select {
 	case err := <-errChan:
 		if err != nil {
-			if routing.IsError(err, routing.ErrOutdated,
-				routing.ErrIgnored) {
+			if graph.IsError(err, graph.ErrOutdated,
+				graph.ErrIgnored) {
 
-				log.Debugf("Router rejected "+
+				log.Debugf("Graph rejected "+
 					"ChannelUpdate: %v", err)
 			} else {
 				return fmt.Errorf("error sending channel "+
@@ -4354,10 +4354,10 @@ func (f *Manager) announceChannel(localIDKey, remoteIDKey *btcec.PublicKey,
 	select {
 	case err := <-errChan:
 		if err != nil {
-			if routing.IsError(err, routing.ErrOutdated,
-				routing.ErrIgnored) {
+			if graph.IsError(err, graph.ErrOutdated,
+				graph.ErrIgnored) {
 
-				log.Debugf("Router rejected "+
+				log.Debugf("Graph rejected "+
 					"AnnounceSignatures: %v", err)
 			} else {
 				log.Errorf("Unable to send channel "+
@@ -4384,10 +4384,10 @@ func (f *Manager) announceChannel(localIDKey, remoteIDKey *btcec.PublicKey,
 	select {
 	case err := <-errChan:
 		if err != nil {
-			if routing.IsError(err, routing.ErrOutdated,
-				routing.ErrIgnored) {
+			if graph.IsError(err, graph.ErrOutdated,
+				graph.ErrIgnored) {
 
-				log.Debugf("Router rejected "+
+				log.Debugf("Graph rejected "+
 					"NodeAnnouncement: %v", err)
 			} else {
 				log.Errorf("Unable to send node "+