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