Taproot Fields for PSBT.

Adds the extra details signing devices need to sign Taproot payments using the shared PSBT file format.

Taproot brought a new kind of signature and a new way of building scripts into an address, which the older PSBT format, the file that carries an unsigned payment, could not describe. These new fields carry Taproot signatures, keys and scripts, so wallets and hardware signers can pass Taproot payments between them for signing.