Implement z_validateaddress RPC

[arya2]

Motivation

Some mining pools use this RPC to check addresses.

Specifications

https://zcash.github.io/rpc/z_validateaddress.html

Designs

We can call the zcash_address crate to validate shielded and unified addresses. (Zebra also has its own transparent address parsing, but we'd be better to just be consistent and use zcash_address for everything.)

We just need to implement these fields:

• isvalid
• address
• type
• address_type (same as type)
• ismine - always false, because Zebra doesn't have a wallet

The Address enum added in #6086 can be extended to convert shielded addresses as well for implementing this RPC.

[mpguerra]

Hey team! Please add your planning poker estimate with Zenhub @arya2 @conradoplg @dconnolly @oxarbitrage @teor2345 @upbqdn

[teor2345]

This is on the critical path for mining pool testing.

[upbqdn]

How do we know we don't have to implement the diversifier and diversifiedtransmissionkey fields described in the spec https://zcash.github.io/rpc/z_validateaddress.html?

[teor2345]

How do we know we don't have to implement the diversifier and diversifiedtransmissionkey fields described in the spec https://zcash.github.io/rpc/z_validateaddress.html?

We don't support Sapling shielded coinbase yet (#5472), and those fields are only used for Sapling. So we could add those fields to the Sapling ticket, if they aren't already there?

[upbqdn]

Even though it's not stated in the spec, Zcashd checks unified addresses. Should we also support those?

[teor2345]

Even though it's not stated in the spec, Zcashd checks unified addresses. Should we also support those?

Maybe as a separate ticket once the unified address PR #6171 merges?

[teor2345]

@upbqdn did you want to open that ticket so we don't forget? It doesn't need to be long, we can fill it in later.

[mpguerra]

yes, I'd rather not block testing and the release on unified addresses. We can add them in after.