Add back form validation

[crutchcorn]

This PR is the primary effort of @aadito123

Fixes #466

Replaces #493 thanks to permissions issues (my fault somehow)

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[codecov-commenter]

Codecov Report

Attention: Patch coverage is 86.95652% with 15 lines in your changes missing coverage. Please review.

Project coverage is 87.53%. Comparing base (c2f9957) to head (3cac019).
Report is 434 commits behind head on main.

Files with missing lines	Patch %	Lines
packages/form-core/src/FormApi.ts	86.48%	12 Missing and 3 partials ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #505      +/-   ##
==========================================
+ Coverage   84.55%   87.53%   +2.98%     
==========================================
  Files           9       19      +10     
  Lines         395      626     +231     
  Branches      109      167      +58     
==========================================
+ Hits          334      548     +214     
- Misses         52       67      +15     
- Partials        9       11       +2     

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