Refactor crate determination in new ethers-macro crate

[sebastinez]

Motivation

Currently when wanting to implement the EIP712 derive macro, one has to import ethers_core as a separate dependency, or declare it like ethers::core as ethers_core.
This is cumbersome and not clean.

Solution

By making use of the convenience function in ethers::contract::abigen::ethers_core_crate() we can compute a path and show it in the derive macro.
By doing this we can avoid this additional ethers_core dependency in external projects.

PR Checklist

• Added Tests
• Added Documentation
• Updated the changelog

[sebastinez]

Hey @gakonst, this should solve the issue with needing to import ethers_core as separate dependency.
Let me know if you have any feedback regarding this PR.

[mattsse]

this would be an opportunity to think about ethers-macros #494 again.
At first, we could simply create it and move the create detection there and then figure out how to proceed.

[gakonst]

Yeah so: Let's make an ethers-macros crate and pull in the crate detection functions there, and use them in both ethers-contract-abigen and ethers-712. Code changes look good otherwise beyond the dependencies.

[sebastinez]

Yeah so: Let's make an ethers-macros crate and pull in the crate detection functions there, and use them in both ethers-contract-abigen and ethers-712. Code changes look good otherwise beyond the dependencies.

Okay no problem!
Will do a push today with these changes

[gakonst]

Amazing. Thank you.

[gakonst]

Should this be optional = true and enabled only if macros is enabled?

[sebastinez]

Yeah that makes sense since it's only used by the macros crate for now