feat(abigen): add MultiAbigen to generate multiple contract bindings

[mattsse]

Motivation

rust-analyzer and intellij still struggle to expand the abigen! macro and fail to provide useful intellisense, this makes it harder to get started with abigen!and usually requires to expand the macro by hand to see what functions are available.

Solution

The new MultiAbigen type can be used to create bindings for several contract at once and generate a new module like this: https://github.com/Gearbox-protocol/liquidation-bot/blob/master/src/bindings/mod.rs

This can be used to generate a module like this once, keep that in repository so that intellisense is available and ensure the CI will fail if the generated code is out of date

PR Checklist

• Added Tests
• Added Documentation
• Updated the changelog

[gakonst]

Nice - wonder if we should create a binary which exposes the functionality that one can easily install to re-generate their bindings? Feels like this is the high level utility we needed to make such a CLI useful.

[mattsse]

Nice - wonder if we should create a binary which exposes the functionality that one can easily install to re-generate their bindings? Feels like this is the high level utility we needed to make such a CLI useful.

I don't know if a cli is appropriate for this feature only, but adding such a cli should be pretty easy.
However, the intended setup would be to run this as in a test to ensure everything is up to date.

What could be useful as well is a workspace template for https://github.com/cargo-generate/cargo-generate