graph: temporarily rename some ChannelGraph methods

Add the `Tx` suffix to both ForEachNodeDirectedChannelTx and
FetchNodeFeatures temporarily so that we free up the original names for
other use. The renamed methods will be removed or unexported in an
upcoming commit. The aim is to have no exported methods on the
ChannelGraph that accept a kvdb.RTx as a parameter.

graph/db/graph_test.go

@@ -3915,7 +3915,7 @@ func BenchmarkForEachChannel(b *testing.B) {
 	}
 }
 
-// TestGraphCacheForEachNodeChannel tests that the ForEachNodeDirectedChannel
+// TestGraphCacheForEachNodeChannel tests that the ForEachNodeDirectedChannelTx
 // method works as expected, and is able to handle nil self edges.
 func TestGraphCacheForEachNodeChannel(t *testing.T) {
 	graph, err := MakeTestGraph(t)
@@ -3952,7 +3952,7 @@ func TestGraphCacheForEachNodeChannel(t *testing.T) {
 
 	getSingleChannel := func() *DirectedChannel {
 		var ch *DirectedChannel
-		err = graph.ForEachNodeDirectedChannel(nil, node1.PubKeyBytes,
+		err = graph.ForEachNodeDirectedChannelTx(nil, node1.PubKeyBytes,
 			func(c *DirectedChannel) error {
 				require.Nil(t, ch)
 				ch = c