lnwallet: create CommitmentBuilder

We define a new struct CommitmentBuilder that will be used to craft the
final commitment transaction based on the current active channel type.

lnwallet/test_utils.go

@@ -324,6 +324,8 @@ func CreateTestChannels(tweaklessCommits bool) (
 	}
 	alicePool.Start()
 
+	obfuscator := createStateHintObfuscator(aliceChannelState)
+
 	bobPool := NewSigPool(1, bobSigner)
 	channelBob, err := NewLightningChannel(
 		bobSigner, bobChannelState, bobPool,
@@ -334,13 +336,13 @@ func CreateTestChannels(tweaklessCommits bool) (
 	bobPool.Start()
 
 	err = SetStateNumHint(
-		aliceCommitTx, 0, channelAlice.stateHintObfuscator,
+		aliceCommitTx, 0, obfuscator,
 	)
 	if err != nil {
 		return nil, nil, nil, err
 	}
 	err = SetStateNumHint(
-		bobCommitTx, 0, channelAlice.stateHintObfuscator,
+		bobCommitTx, 0, obfuscator,
 	)
 	if err != nil {
 		return nil, nil, nil, err