FIO-9783: evaluator refactor

[brendanbond]

Link to Jira Ticket

https://formio.atlassian.net/browse/FIO-9783

Description

We've identified a bottleneck in the way we perform form validation in our Enterprise Server - creating VM contexts per request and executing the entire form orchestration pipeline in those contexts turns out to be kind of slow and expensive. To mitigate this, I've changed the way the Evaluator class is leveraged: instead of a static singleton class, it is now a mutable class instance that can be extended and overridden as needed, giving us access to things like constructors.

On a granular level, this PR merely adopts the new singleton instance Evaluator and cleans up the utilities import/export structure.

Breaking Changes / Backwards Compatibility

This introduces a fair amount of risk (although tests are passing) but there are certainly not any intentional breaking changes in this PR.

Dependencies

@formio/core#245

How has this PR been tested?

Tests are passing.

Checklist:

• I have completed the above PR template
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation (if applicable)
• My changes generate no new warnings
• My changes include tests that prove my fix is effective (or that my feature works as intended)
• New and existing unit/integration tests pass locally with my changes
• Any dependent changes have corresponding PRs that are listed above