multi/refactor: add RouteRequest to hold FindRoute parameters

This commit introduces a single struct to hold all of the parameters
that are passed to FindRoute. This cleans up an already overloaded
function signature and prepares us for handling requests with blinded
routes where we need to perform some additional processing on our
para (such as extracting the target node from the blinded path).

lnrpc/routerrpc/router_backend_test.go

@@ -7,10 +7,8 @@ import (
 	"testing"
 
 	"github.com/btcsuite/btcd/btcutil"
-	"github.com/lightningnetwork/lnd/channeldb"
 	"github.com/lightningnetwork/lnd/lnrpc"
 	"github.com/lightningnetwork/lnd/lnwire"
-	"github.com/lightningnetwork/lnd/record"
 	"github.com/lightningnetwork/lnd/routing"
 	"github.com/lightningnetwork/lnd/routing/route"
 	"github.com/stretchr/testify/require"
@@ -122,24 +120,23 @@ func testQueryRoutes(t *testing.T, useMissionControl bool, useMsat bool,
 		}
 	}
 
-	findRoute := func(source, target route.Vertex,
-		amt lnwire.MilliSatoshi, _ float64,
-		restrictions *routing.RestrictParams, _ record.CustomSet,
-		routeHints map[route.Vertex][]*channeldb.CachedEdgePolicy,
-		finalExpiry uint16) (*route.Route, float64, error) {
+	findRoute := func(req *routing.RouteRequest) (*route.Route, float64,
+		error) {
 
-		if int64(amt) != amtSat*1000 {
+		if int64(req.Amount) != amtSat*1000 {
 			t.Fatal("unexpected amount")
 		}
 
-		if source != sourceKey {
+		if req.Source != sourceKey {
 			t.Fatal("unexpected source key")
 		}
 
+		target := req.Target
 		if !bytes.Equal(target[:], destNodeBytes) {
 			t.Fatal("unexpected target key")
 		}
 
+		restrictions := req.Restrictions
 		if restrictions.FeeLimit != 250*1000 {
 			t.Fatal("unexpected fee limit")
 		}
@@ -172,6 +169,7 @@ func testQueryRoutes(t *testing.T, useMissionControl bool, useMsat bool,
 			t.Fatal("unexpected dest features")
 		}
 
+		routeHints := req.RouteHints
 		if _, ok := routeHints[hintNode]; !ok {
 			t.Fatal("expected route hint")
 		}
@@ -187,7 +185,9 @@ func testQueryRoutes(t *testing.T, useMissionControl bool, useMsat bool,
 		}
 
 		hops := []*route.Hop{{}}
-		route, err := route.NewRouteFromHops(amt, 144, source, hops)
+		route, err := route.NewRouteFromHops(
+			req.Amount, 144, req.Source, hops,
+		)
 
 		return route, expectedProb, err
 	}