contraccourt+input: create resolver for timeout second level

In this commit we make the sweeper handle second level transactions for
HTLC timeout resolvers for anchor channels.

input/input.go

@@ -305,6 +305,43 @@ func (i *HtlcSecondLevelAnchorInput) CraftInputScript(signer Signer,
 	}, nil
 }
 
+// MakeHtlcSecondLevelTimeoutAnchorInput creates an input allowing the sweeper
+// to spend the HTLC output on our commit using the second level timeout
+// transaction.
+func MakeHtlcSecondLevelTimeoutAnchorInput(signedTx *wire.MsgTx,
+	signDetails *SignDetails, heightHint uint32) HtlcSecondLevelAnchorInput {
+
+	// Spend an HTLC output on our local commitment tx using the
+	// 2nd timeout transaction.
+	createWitness := func(signer Signer, txn *wire.MsgTx,
+		hashCache *txscript.TxSigHashes,
+		txinIdx int) (wire.TxWitness, error) {
+
+		desc := signDetails.SignDesc
+		desc.SigHashes = txscript.NewTxSigHashes(txn)
+		desc.InputIndex = txinIdx
+
+		return SenderHtlcSpendTimeout(
+			signDetails.PeerSig, signDetails.SigHashType, signer,
+			&desc, txn,
+		)
+	}
+
+	return HtlcSecondLevelAnchorInput{
+		inputKit: inputKit{
+			outpoint:    signedTx.TxIn[0].PreviousOutPoint,
+			witnessType: HtlcOfferedTimeoutSecondLevelInputConfirmed,
+			signDesc:    signDetails.SignDesc,
+			heightHint:  heightHint,
+
+			// CSV delay is always 1 for these inputs.
+			blockToMaturity: 1,
+		},
+		SignedTx:      signedTx,
+		createWitness: createWitness,
+	}
+}
+
 // MakeHtlcSecondLevelSuccessAnchorInput creates an input allowing the sweeper
 // to spend the HTLC output on our commit using the second level success
 // transaction.