Add separate PSBTError enum instead of reusing TransactionError enum for PSBT
operations, and drop unused error codes. The error codes returned by PSBT
operations and transaction broadcast functions mostly do not overlap, so using
an unified enum makes it harder to call any of these functions and know which
errors actually need to be handled.
Define PSBTError in the common library because PSBT functionality is
implemented in the common library and used by both the node (for rawtransaction
RPCs) and the wallet.
