Closed
Description
When using PSBT to sign taproot outputs, extra data needs to be communicated in the form of the control block, input values+scripts, and also which sighash type/extension to use. These new fields are defined in BIP 371. To support more generalized taproot tools/applications built on top of lnd, we should extend our PSBT handling an validation to understand, populate, and validate these fields.
Note that much of this work will actually be in btcwallet and btcd/btcutil/psbt, but we're tracking it here for cross-repo compatibility.
Related to #6267.