graph/db: use PreferHighest for channel fetches and add GetVersions wrappers

Switch FetchChannelEdgesByID and FetchChannelEdgesByOutpoint on
ChannelGraph to use the PreferHighest store variants so that callers
get the highest available gossip version without needing to specify
one.

Also add GetVersionsBySCID and GetVersionsByOutpoint convenience
wrappers on ChannelGraph that delegate to the corresponding Store
methods.

Author: ellemouton

graph/db/graph.go

@@ -773,26 +773,39 @@ func (c *ChannelGraph) FetchChanInfos(ctx context.Context,
 }
 
 // FetchChannelEdgesByOutpoint attempts to lookup directed edges by funding
-// outpoint.
+// outpoint, returning the highest available gossip version.
 func (c *ChannelGraph) FetchChannelEdgesByOutpoint(ctx context.Context,
 	op *wire.OutPoint) (
 	*models.ChannelEdgeInfo, *models.ChannelEdgePolicy,
 	*models.ChannelEdgePolicy, error) {
 
-	return c.db.FetchChannelEdgesByOutpoint(
-		ctx, lnwire.GossipVersion1, op,
-	)
+	return c.db.FetchChannelEdgesByOutpointPreferHighest(ctx, op)
 }
 
-// FetchChannelEdgesByID attempts to lookup directed edges by channel ID.
+// FetchChannelEdgesByID attempts to lookup directed edges by channel ID,
+// returning the highest available gossip version.
 func (c *ChannelGraph) FetchChannelEdgesByID(ctx context.Context,
 	chanID uint64) (
 	*models.ChannelEdgeInfo, *models.ChannelEdgePolicy,
 	*models.ChannelEdgePolicy, error) {
 
-	return c.db.FetchChannelEdgesByID(
-		ctx, lnwire.GossipVersion1, chanID,
-	)
+	return c.db.FetchChannelEdgesByIDPreferHighest(ctx, chanID)
+}
+
+// GetVersionsBySCID returns the list of gossip versions for which a channel
+// with the given SCID exists in the database.
+func (c *ChannelGraph) GetVersionsBySCID(ctx context.Context,
+	chanID uint64) ([]lnwire.GossipVersion, error) {
+
+	return c.db.GetVersionsBySCID(ctx, chanID)
+}
+
+// GetVersionsByOutpoint returns the list of gossip versions for which a channel
+// with the given funding outpoint exists in the database.
+func (c *ChannelGraph) GetVersionsByOutpoint(ctx context.Context,
+	op *wire.OutPoint) ([]lnwire.GossipVersion, error) {
+
+	return c.db.GetVersionsByOutpoint(ctx, op)
 }
 
 // PutClosedScid stores a SCID for a closed channel in the database.