Support Client-Side Validation

[dillonredding]

When submitting an action, there should be an option to enable/customize client-side validation.

abstract class ValidationResult;

class PositiveValidationResult extends ValidationResult;

class NegativeValidationResult extends ValidationResult {
  invalidFields: Field[];
}

type Validator = (fields: Field[]) => ValidationResult;

// custom validator
await submit(action, {
  validator: (fields: Field[]): ValidationResult => {
    const invalidFields: Field[] = [];
    // validate fields (e.g., based on `type`)
    return invalidFields.length > 0
      ? new NegativeValidationResult(invalidFields)
      : new PositiveValidationResult();
  }
});

// disable validation
await submit(action, { validate: false });

By default, we could provide a default validator that functions similar to HTML's client-side validation.