This PR enables support for BIP-322, the sign/verify message upgrade.
Fixes #10542.
This PR is greatly simplified and is supposed to have one or more follow-up PRs to complete functionality.
In this PR:
- signing using single key (any type)
- verifying any signed message (auto-detects BIP-322 vs legacy)
Missing features/limitations:
- proof of funds (i.e. additional inputs) support
- multisig or other custom address type support (I need feedback on how to do this; I assume some psbt thing would be good?)
- (RPC) format is restricted to SIMPLE mode now; it may eventually be LEGACY, SIMPLE, or FULL. (In some cases, it will use FULL format but this is not selectable yet.)
- timelock support