Merge #465: Add PsbtOutputExt::update_with_descriptor

9a57e00 Ensure there are no duplicated leaf hashes in `tap_key_origins` (Alekos Filini)
1bbd13b Allow `non_witness_utxo` for segwit PSBTs (Alekos Filini)
9f63165 Append bip32 derivations instead of replacing the map entirely (Alekos Filini)
f46830c Add tests for `PsbtExt::update_output_with_descriptor` (Alekos Filini)
3148fb3 Correct error description for `UtxoUpdateError::MissingInputUtxo` (Alekos Filini)
03c25ec Add `PsbtOutputExt::update_with_descriptor` (Alekos Filini)

Pull request description:

  This essentially mirrors `PsbtInputExt::update_with_descriptor` but it works on PSBT outputs.

  To avoid code duplication, the current logic that deals with PSBT inputs has been generalized to handle both input and outputs with a new internal `PsbtFields` trait.

  -----

  I hope it's not too late to get this PR in the new 8.0 release (cc #462)

ACKs for top commit:
  apoelstra:
    ACK 9a57e00
  sanket1729:
    ACK 9a57e00. Not completely happy with internal trait abstraction. I may work on a future PR to abstract that into a function that takes 1) script pubkey and 2) descriptor and outputs the relevant fields that are added to the psbt.

Tree-SHA512: 595485b8aa6db665a120ff756c522b8e81858c06bf86dbda25e5b742f10ad537481351c0111b5f0946919f90f7784c8ff2c2e99b9f403f4607723f46ac608d38

Author: sanket1729