lnwallet: update to genRemoteHtlcSigJobs to generate taproot jobs

In this commit, we update the genRemoteHtlcSigJobs function to be able
to generate taproot jobs. We also modify the sigpool to now use a
input.Signature everywhere. This'll allow us to pass around both ECDSA
and Schnorr signatures via the same interface.

We use a tapscript sighash in this case, as all the HTLC spends will
actually be script path spends.

lnwallet/sigpool.go

@@ -113,8 +113,6 @@ type SignJobResp struct {
 	Err error
 }
 
-// TODO(roasbeef); fix description
-
 // SigPool is a struct that is meant to allow the current channel state
 // machine to parallelize all signature generation and verification. This
 // struct is needed as _each_ HTLC when creating a commitment transaction
@@ -206,7 +204,11 @@ func (s *SigPool) poolWorker() {
 				}
 			}
 
+			// Use the sig mapper to go from the input.Signature
+			// into the serialized lnwire.Sig that we'll send
+			// across the wire.
 			sig, err := lnwire.NewSigFromSignature(rawSig)
+
 			select {
 			case sigMsg.Resp <- SignJobResp{
 				Sig: sig,