fix: #3593600 Prevent duplicate error_notempty for required string fields with minLength >= 1

When a JSON Schema string field declares both 'required' at the parent object level and 'minLength: 1' on the property, two validators independently emit error_notempty for the same field path: the built-in minLength validator (property: 'minLength') and the custom patternkitRequiredStringValidator (property: 'required'). _removeDuplicateErrors deduplicates on (message, path, property), so the differing property values cause the duplicate to survive.

Guard condition: skip emitting from the custom validator when fieldSchema.minLength is a number >= 1. The built-in validator already covers this case with identical wording.

Closes #3593600