Deprecation: #85802 - Move FlexFormService from EXT:extbase to EXT:core 

See forge#85802

Description 

Move FlexFormService from EXT:extbase to EXT:core.

Impact 

The PHP class \TYPO3\CMS\Extbase\Service\FlexFormService has been moved from the system extension extbase to core. The PHP class has been renamed to \TYPO3\CMS\Core\Service\FlexFormService.

Affected Installations 

Any TYPO3 installation where this PHP class is in use within a TYPO3 extension.

Migration 

Use the new namespace to reference the \TYPO3\CMS\Core\Service\FlexFormService.