Add validatingFields to formState return from useRemixForm to be compatible with react-hook-form 7.51.0

[AdiRishi]

Description

This PR adds compatibility with react-hook-form version 7.51.0

Fixes #84

Type of change

This is mainly a bugfix. However I'm not sure how this would behave if used with a version of react-hook-form that did not return validatingFields from state. It should be fine, that value will just be undefined.

• [X] Bug fix (non-breaking change which fixes an issue)

How Has This Been Tested?

I've updated the unit tests to reflect the new field being added.

Checklist:

• [X] My code follows the guidelines of this project
• [X] I have performed a self-review of my own code
• [X] I have commented my code, particularly in hard-to-understand areas
• [X] I have made corresponding changes to the documentation
• [X] My changes generate no new warnings or errors
• [X] I have added tests that prove my fix is effective or that my feature works
• [X] New and existing unit tests pass locally with my changes
• [X] Any dependent changes have been merged and published in downstream modules