[BUGFIX] Import full namespace of TYPO3\CMS\Core\Resource\ProcessedFile

The class ProcessedFile in ApplicationThumbnail service is used without
having its namespace imported which leads to a fatal error.

Releases: 3.0
Resolves: #58736
Change-Id: Id75bec9f3feb979b05c381dfc02fcec6e7404f1f
Reviewed-on: https://review.typo3.org/30030
Reviewed-by: Fabien Udriot
Tested-by: Fabien Udriot