Applies to both `ecdsa::Signature` and `taproot::Signature`.
Re-name the `Signature` fields with more descriptive names. The
names used were decided upon in the issue discussion.
Impove rustdocs while we are at it.
Note, the change to `sign-tx-segwit-v0` is refactor only, the diff does
not show it but we have a local variable already called `sighash_type`
that is equal to `EcdsaSighashType::All`.
Includes a function argument rename as well, just to be uniform.
Fix: #2139
271b45299f