Feature: #80263 - Add a new signal slot for user switch

See Issue #80263

Description

A new signal is emitted once an admin user switches into another user via the Switch-To functionality within TYPO3 core.

Use the following code to use the signal

$dispatcher = \TYPO3\CMS\Core\Utility\GeneralUtility::makeInstance(\TYPO3\CMS\Extbase\SignalSlot\Dispatcher::class);
$dispatcher->connect(
    \TYPO3\CMS\Beuser\Controller\BackendUserController::class,
    'switchUser',
    \MyVendor\MyExtension\Slots\BackendUserController::class,
    'switchUser'
);