routing: extend path finding to be TLV-EOB aware, allow dest TLV records

In this commit, we extend the path finding to be able to recognize when
a node needs the new TLV format, or the legacy format based on the
feature bits they expose. We also extend the `LightningPayment` struct
to allow the caller to specify an arbitrary set of TLV records which can
be used for a number of use-cases including various variants of
spontaneous payments.

routing/payment_session_test.go

@@ -26,7 +26,11 @@ func TestRequestRoute(t *testing.T) {
 
 		path := []*channeldb.ChannelEdgePolicy{
 			{
-				Node: &channeldb.LightningNode{},
+				Node: &channeldb.LightningNode{
+					Features: lnwire.NewFeatureVector(
+						nil, nil,
+					),
+				},
 			},
 		}