feat: allow configurable hash-to-field function for Groth16 Solidity verifier

[ivokub]

Description

To allow different compatibility, it is beneficial to support different hash-to-field functions to hash the commitments to field in Solidity contract. This PR extends the ExportSolidity method to take in options which allow changing the functions. Later, we could possibly use the extendability to also change the HTF function for PLONK Solidity verifier, but keeping unchanged for now.

Also added TargetSolidity options for the prover and verifier which chooses all the parameters optimally for Solidity verifier. For PLONK prover it is currently no-op, but this allows more simply to change the hash functions we use within (with corresponding little gas savings).

Ref #1094

Type of change

• New feature (non-breaking change which adds functionality)

How has this been tested?

In package backend/solidity:

• TestNoCommitment
• TestSingleCommitment
• TestTwoCommitments

And the subtests

How has this been benchmarked?

Not benchmarked, only changes Solidity verifier

Checklist:

• I have performed a self-review of my code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• I have added tests that prove my fix is effective or that my feature works
• I did not modify files generated from templates
• golangci-lint does not output errors locally
• New and existing unit tests pass locally with my changes
• Any dependent changes have been merged and published in downstream modules