FIO-4112: Integrate @formio/core validation engine to renderer + many other code cleanup.

[travist]

Link to Jira Ticket

https://formio.atlassian.net/browse/FIO-4112

Description

This change refactors the validation engine to use @formio/core validator.

Dependencies

This PR depends on latest 2.x of @formio/core.

How has this PR been tested?

A bunch of automated tests already include tests for the renderer.

Checklist:

• 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