contractcourt+server: settle invoice for on-chain HTLC sweep

In this commit, we extend the htlcSuccessResolver to settle the invoice,
if any, of the corresponding on-chain HTLC sweep. This ensures that the
invoice state is consistent as when claiming the HTLC "off-chain".

server.go

@@ -728,7 +728,8 @@ func newServer(listenAddrs []net.Addr, chanDB *channeldb.DB, cc *chainControl,
 		DisableChannel: func(op wire.OutPoint) error {
 			return s.announceChanStatus(op, true)
 		},
-		Sweeper: s.sweeper,
+		Sweeper:       s.sweeper,
+		SettleInvoice: s.invoices.SettleInvoice,
 	}, chanDB)
 
 	s.breachArbiter = newBreachArbiter(&BreachConfig{