With this commit we bump the github.com/btcd/btcec/v2 library to v2.3.2
which implements the MuSig2 BIP version v1.0.0rc2. With this the
github.com/btcsuite/btcd/btcec/v2/schnorr/musig2 package becomes
v1.0.0rc2 and the github.com/lightningnetwork/lnd/internal/musig2v040
stays at the old v0.4.0 version.
To allow us to properly test all test vectors, we can't default to true
on key sorting. Instead we add a parameter to the input package and move
the default value to the RPC server.
As a preparation for making it possible to version switch calls to the
MuSig2 API, we move some of the calls to the input package where in a
future commit we'll call the corresponding code in the correct package.
