[chain] ABI-like support for Realm / Package requests / responses

[zivkovicmilos]

Description

This effort covers the introduction of an ABI-like standard for Gno Realm / Packages.

Copied from an issue on the Gno repo:
Gno.land Realms expose public methods that can be queried off-chain by client applications. The problem lies in the fact that the responses of specific public methods can be different from primitive types in Golang, for example a struct or a type alias.
In this case, the response the clients will receive will contain the raw value and the type of response (ex my response MyComplexType), leaving the clients to do custom parsing on their own.

There is also the parallel problem of constructing method calls. Clients need to know upfront what kind of data needs to be packaged as the arguments of a public Realm method.
Ethereum Solidity Smart Contracts provide a contract ABI (essentially a JSON specification), which the clients can utilize to understand how to call Smart Contract methods, and what kinds of responses to expect.

Successful outcome of this effort:

• There is a defined standard for Realms / Packages that clients can use to construct requests / parse responses
• There is an implemented tool that can generate this specification (in JSON for example) based on an input Realm / Package

[thehowl]

Are we not doing this in #1776?

[thehowl]

I mean, ok, this issue is about making a spec for it, but I'm still surprised to see that it wasn't even mentioned as an effort

Having good cross-references to other issues is one of the few good things about our issue tracker, let's try to keep it that way :)

[leohhhn]

@jeronimoalbi @salmad3 pinging just for visibility. Could be a related effort to gnoschema.

[n0izn0iz]

not sure where to put this:

re: encoding structs in transaction result

solidity supports returning structs via ABIEncoderV2
maybe we can learn from that effort