multi: update GenTaprootFundingScript to pass tapscript root

In most cases, we won't yet be passing a root. The option usage helps us keep the control flow mostly unchanged.

contractcourt/chain_watcher.go

@@ -308,7 +308,7 @@ func (c *chainWatcher) Start() error {
 	)
 	if chanState.ChanType.IsTaproot() {
 		c.fundingPkScript, _, err = input.GenTaprootFundingScript(
-			localKey, remoteKey, 0, fn.None[chainhash.Hash](),
+			localKey, remoteKey, 0, chanState.TapscriptRoot,
 		)
 		if err != nil {
 			return err

funding/manager.go

@@ -24,7 +24,6 @@ import (
 	"github.com/lightningnetwork/lnd/channeldb"
 	"github.com/lightningnetwork/lnd/channeldb/models"
 	"github.com/lightningnetwork/lnd/discovery"
-	"github.com/lightningnetwork/lnd/fn"
 	"github.com/lightningnetwork/lnd/graph"
 	"github.com/lightningnetwork/lnd/input"
 	"github.com/lightningnetwork/lnd/keychain"
@@ -2900,7 +2899,7 @@ func makeFundingScript(channel *channeldb.OpenChannel) ([]byte, error) {
 	if channel.ChanType.IsTaproot() {
 		pkScript, _, err := input.GenTaprootFundingScript(
 			localKey, remoteKey, int64(channel.Capacity),
-			fn.None[chainhash.Hash](),
+			channel.TapscriptRoot,
 		)
 		if err != nil {
 			return nil, err

graph/builder.go

@@ -1146,6 +1146,8 @@ func makeFundingScript(bitcoinKey1, bitcoinKey2 []byte,
 			return nil, err
 		}
 
+		// TODO(roasbeef): add tapscript root to gossip v1.5
+
 		return fundingScript, nil
 	}