Merge bitcoin/bitcoin#23578: Add external signer taproot support

796b020c37 wallet: add taproot support to external signer (Sjors Provoost)

Pull request description:

  Builds on #22558 (merged on 2022-06-28).

  [HWI 2.1.0](https://github.com/bitcoin-core/HWI/releases/tag/2.1.0) or newer is required to import and use taproot descriptors. Older versions will work, but won't import a taproot descriptor.

  Tested with HWI 2.1.1:
  * Trezor T (firmware v2.5.1) on Signet: signs, change detection works
  * Ledger Nano S (firmware 2.1.0, Bitcoin app 2.0.6): signs, change detection works

  Only the most basic `tr(key)` descriptor is supported, script path spending is completely untested (if it works at all).

ACKs for top commit:
  jb55:
    utACK 796b020c37
  achow101:
    ACK 796b020c37

Tree-SHA512: 6dcb7eeb45421a3bbf2bdabeacd29979867db69077d7bf192bb77faa4bfefe446487b8df07bc40f9457009a88e598bdc09f769e6106fed2833ace7ef205a157a

src/external_signer.cpp

@@ -81,6 +81,9 @@ bool ExternalSigner::SignTransaction(PartiallySignedTransaction& psbtx, std::str
         for (const auto& entry : input.hd_keypaths) {
             if (parsed_m_fingerprint == MakeUCharSpan(entry.second.fingerprint)) return true;
         }
+        for (const auto& entry : input.m_tap_bip32_paths) {
+            if (parsed_m_fingerprint == MakeUCharSpan(entry.second.second.fingerprint)) return true;
+        }
         return false;
     };