Add sidechain-specific features

[mvadari]

I'd like to add two features related to sidechains to xrpl4j:

• A new RPC, federator_info, which provides information about the mainchain-sidechain bridge federators
• A new method/builder that helps developers create a cross-chain transaction. The method takes a payment transaction and the sidechain destination address and adds the sidechain destination address (encoded in hex) as a memo.

Analogous xrpl.js issue: XRPLF/xrpl.js#1940
Analogous xrpl-py issue: XRPLF/xrpl-py#366

[sappenin]

Thanks @mvadari , this is a great suggestion!

[nkramer44]

@mukulljangid Do you mind taking this on?

The new federator_info RPC should require new XrplRequest and XrplResult immutables. I would mark them as @Beta just in case the API changes between now and launch.

As for the helper method -- I wonder if it would make sense to add a method/field to the Payment immutable Optional<Address> crossChainDestination(). This method wouldn't get serialized to JSON, but if it's present we could easily set the memo field to the hex representation of the destination address. This would make cross-chain stuff easy without having to introduce a new util or service class. @mukulljangid @sappenin How does that sound?

[mukulljangid]

Thanks @nkramer44! Sounds good to me! I was a bit skeptical about adding a new util. This approach should work!

[mvadari]

The sidechain design has been greatly updated now.

There are 7 new transaction types. While there aren't any more RPCs, some of the RPCs (ledger_entry, account_objects) have more filters.

References:

• rippled PR: XLS-38d: XChainBridge (side chains) rippled#4292
• xrpl.js PR: feat: add support for current sidechain design xrpl.js#2039
• xrpl-py PR: feat: add support for XLS-38d xrpl-py#417