Fix overlapped Identity name definition

Fix "Cannot use eZ\Publish\SPI\User\Identity as Identity because the name is already in use in /.../vendor/ezsystems/ezpublish-kernel/eZ/Publish/Core/MVC/Symfony/Security/User/HashGenerator.php on line 13"
Merge pull request #776 from rolebi/master

EZP-22481: Fix overlapped Identity name definition