Make ResetCommand go through APISolver (#6172)

Make ResetCommand go through APISolver (#6172)

This PR changes ResetCommand to not call SmtEngine::reset but instead reconstruct the api::Solver object. This makes SmtEngine::reset obsolete and removes it, and moves the original options from SmtEngine to api::Solver.
The motivation for this change is twofold:

The ResetCommand should not use SmtEngine directly, but only through the API (i.e. Solver).
As soon as the statistics data lives within the registry, we need to re-register statistics after resetting the SmtEngine. We can now do this within the api::Solver constructor.