Feature: #91719 - Custom error messages in RegularExpressionValidator

Description

The RegularExpressionValidator can now return a custom validation error message to help the user providing valid input.

Impact

A new option errorMessage has been introduced to the validator.

Example:

class MyModel extends \TYPO3\CMS\Extbase\DomainObject\AbstractEntity
{
    /**
     * @var string
     * @TYPO3\CMS\Extbase\Annotation\Validate(
     *    "RegularExpression",
     *    options={
     *       "regularExpression": "/^SO[0-9]$/",
     *       "errorMessage": "explain how to provide a valid value"
     *    }
     * )
     */
    protected $customField;
}

It is also possible to provide a translation key to render a localized message:

class MyModel extends \TYPO3\CMS\Extbase\DomainObject\AbstractEntity
{
    /**
     * @var string
     * @TYPO3\CMS\Extbase\Annotation\Validate(
     *    "RegularExpression",
     *    options={
     *       "regularExpression": "/^SO[0-9]$/",
     *       "errorMessage": "LLL:EXT:my_extension/path/to/xlf:translation.key"
     *    }
     * )
     */
    protected $customField;
}

If no errorMessage is provided, the default message will be displayed in case of a validation error.