Jack Grigg

Rebased on master after #2816 merged.

Extracted most of the small PRs from here into #4994. I'll rebase this PR on master after that is reviewed and merged (as the remaining PRs here require those PRs).

I extracted more commits into #4996 and #4997; this PR is now basically just bitcoin/bitcoin#7129. I'll rebase this once #4997 merges.

bitcoin/bitcoin#7125 was extracted into #5265, so this PR is now exactly bitcoin/bitcoin#7129 (plus necessary small follow-ons).

@zkbot try

Rebased to fix merge conflicts (and bump the protocol version it would activate on if we merged it).

> 1. Be able to parse a user string from an "address" field, and identify what type of address it is. Like if the user types in "ztestsapling....." into an...

Thinking about this again. I think I'd prefer one of the following approaches: - We get address types into `zcash_primitives` (we currently have been developing types in `zcash_client_backend` but will...

I've had this PR backported in #2225 for well over two years now. I really need to cut that PR down to size 😬

@zkbot try