Experimentally integrate C++ Witness Generator

[oskarth]

Problem

See https://github.com/oskarth/mopro/issues/109

Suggested approach

Suggested course of action: We try for C++ witness gen as experimental feature and create a shared branch?PR in mopro for doing an MVP integration, both Vivian and Florent can collab on it together there. The branch/PR can be ugly and breaking and we can clean it up later.

Once it works in MVP form it should be trivial to then integrate with proof-of-passport. This would also allow us to work together on it and sharing code/effort

Details

• https://github.com/0xPolygonID/witnesscalc
• https://github.com/rarimo/FreedomTool
• https://github.com/rarimo/FreedomToolAndroid

Also relevant: https://github.com/oskarth/mopro/issues/44

Acceptance criteria

• Understanding in diff in terms of interface when using C++ version (e.g. require rapidsnark?)
• C++ witness generator integrated and working end to end (dirty)
• Integrated with feature flag cleanly