We need to export the enum as it'll now be used in areas such as the
chan closer.

…to accept

In this commit, we add a new NewCommitState struct. This preps us for
the future change wherein a partial signature is also added to the mix.
All related tests and type signatures have also been updated
accordingly.

…TLCs

…ation

In this commit, we update the channel state machine with a new set of
functional options that can be used to create/set the musig session
state. When a channel is made during the funding process, the set of
nonces we want to use is already known, so we allow them to be passed
in. Similarly, once the channel is confirmed, then we'll need to create
another channel instance that this times carries the newly generated
nonces to send along side funding_locked.

We also add some utility methods to permit callers to properly generate
nonces in the various contexts.

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.

In this commit, we update the genHtlcSigValidationJobs function to be
taproot aware. As we actually need a schnorr signature for the taproot
validation, we need to coerce the entire wire type into a schnorr sig
with the ForceSchnorr() method.

In this commit, we update the co-op close flow to support the new musig2
keyspend flow. We'll use some new functional options to allow a caller
to pass in an active musig2 session. If this is present, then we'll use
that to complete the musig2 flow by signing with a partial signature,
and then ultimately combining the signatures at the end.

In this commit, we fix a bug in the `deriveMusig2Shachain` function
where it didn't actually use the passed in revocation root as part of
the hmac invocation.

We also modify the function to be more generally useable as well, as now
the caller can just pass in the revocation root things should be derived
from.

In this commit, we update the ChanSyncMsg to populate nonce information.
With this change, we can now hide nonce generation further down in the
pipeline and ensure that all callers will have the expected fields
populated.

Before this commit, we would conditionally generate nonces in
RevokeCurrentCommitment. We move this to generateRevocation as this is
called when doing channel sync, and we want to make sure we send the
correct set of nonces.

In this commit, we update the logic to handle nonce init in
ProcessChanSyncMsg. Once a channel is already open, this is where we'll
get the new nonce data from the remote party we'll use to gain the nonce
we need to sign for their next state.