[BUGFIX] Avoid deprecated FILTER_SANITIZE_STRING in TextValidator

The filter_var() filter FILTER_SANITIZE_STRING is
deprecated as of PHP 8.1.

Extbase TextValidator uses it. Goal of the text
validator is to allow most 'casual' characters
and strings as long as they don't contain HTML.

The path switches to strip_tags() to validate.
Tests are refactored and extended to show more cases.

https://wiki.php.net/rfc/deprecations_php_8_1

Change-Id: Ifbf3de7a7200512d1281b694a7a6c2f8fb3ac781
Resolves: #95768
Releases: master
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/71968


Tested-by: Jochen <rothjochen@gmail.com>
Tested-by: core-ci <typo3@b13.com>
Tested-by: Anja Leichsenring <aleichsenring@ab-softlab.de>
Reviewed-by: Jochen <rothjochen@gmail.com>
Reviewed-by: Anja Leichsenring <aleichsenring@ab-softlab.de>