export-abi support for the new inheritance model

[diegoximenes]

Description

Resolves NIT-3911

This PR includes the following changes:

• export-abi support for the new inheritance model
• Run clippy individually for export-abi. export-abi considerably changes code output, so it is advisable to run it separately.
• ci/build_and_test.sh doesn't run with export-abi. From now on, to test the export-abi feature, we solely rely on the exported abi comparison procedure deployed by the integration test CI step.

What is missing:

• export-abi support for associated types. Filed a linear ticket for that.

Checklist

• I have documented these changes where necessary.
• I have read the DCO and ensured that these changes comply.
• I assign this work under its open source licensing.

[alexandrosfilios]

Maybe very edge case, but in theory we could implement the same generic interface twice (for different generics), e.g.

impl Trait1<String> for Callee {}

impl Trait1<U256> for Callee {}

Then we could either re-define the attribute as

#[implements(Trait1<U256> as Trait1Number, Trait1<String> as Trait1String)]

That would require also some renaming of the methods though. Maybe it would be simpler to return an error if it is the case, or at least document it in the README to avoid the scenario.