feat: add groth16 commitment verifier

[ahmetyalp]

Testing utilities for Consensys/gnark#1063

[ivokub]

cc @gbotrel - I do not have maintainer rights for the repo.

[ivokub]

In general is good, but I'll try to think if we can merge the templates so that wouldn't have different templates for commitment and non-commitment variants. And imo we can also deduce the number of commitments from verification key for example.

I'll try to push some changes after I get maintainer rights.

[ivokub]

I merged the templates with conditional case in case there are commitments for Groth16. Even though I'd prefer not to have --commitments arguments (as it should be deducible from the verification key or the proof itself), then there is too big mismatch between PLONK and Groth16 Solidity verifier APIs to have a nice unified implementation. I'll open another issue to try to unify the APIs (for example having in G16 Verify proof input as bytes similarly as for PLONK). I think we can go for now as is and then try to refactor/unify later in separate PRs.

[ivokub]

@ahmetyalp - can you have a look at my changes and let me know if looks good? I'll then go ahead with merging.

[ivokub]

I think it is good for now to merge. Thanks for the contribution! I'll continue with the PR Consensys/gnark#1063