As Extbase does no longer guess class names from extension
keys and vendor names, method ExtensionUtility::configurePlugin
does no longer accept providing a vendor name.

The same applies as well for parameter $extensionName of method
ExtensionUtility::registerPlugin. The vendor information is
not used at all and must be ommitted in the future.

The former syntax

   \TYPO3\CMS\Extbase\Utility\ExtensionUtility::registerPlugin(
       'TYPO3.CMS.Form',
       'Formframework',
       'Form',
       'content-form',
   );

has to be converted to

   \TYPO3\CMS\Extbase\Utility\ExtensionUtility::registerPlugin(
       'Form',
       'Formframework',
       'Form',
       'content-form',
   );

Releases: master
Resolves: #88995
Change-Id: I247df236d41c24a6ce5f58164f127671237ddf28
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/61522


Tested-by: TYPO3com <noreply@typo3.com>
Tested-by: Anja Leichsenring <aleichsenring@ab-softlab.de>
Tested-by: Jan Stockfisch <typo3@jan-stockfisch.de>
Tested-by: Daniel Goerz <daniel.goerz@posteo.de>
Reviewed-by: Anja Leichsenring <aleichsenring@ab-softlab.de>
Reviewed-by: Jan Stockfisch <typo3@jan-stockfisch.de>
Reviewed-by: Daniel Goerz <daniel.goerz@posteo.de>