[FEATURE] Migrate various Signals to PSR-14 events in system extensions

The following new PSR-14 events are added:

TYPO3\CMS\Core\Configuration\Event\ModifyLoadedPageTsConfigEvent
TYPO3\CMS\Backend\Authentication\Event\SwitchUserEvent
TYPO3\CMS\Backend\Controller\Event\BeforeFormEnginePageInitializedEvent
TYPO3\CMS\Backend\Controller\Event\AfterFormEnginePageInitializedEvent
TYPO3\CMS\Backend\LoginProvider\Event\ModifyPageLayoutOnLoginProviderSelectionEvent
TYPO3\CMS\Impexp\Event\BeforeImportEvent
TYPO3\CMS\Install\Service\Event\ModifyLanguagePackRemoteBaseUrlEvent
TYPO3\CMS\Linkvalidator\Event\BeforeRecordIsAnalyzedEvent
TYPO3\CMS\Seo\Event\ModifyUrlForCanonicalTagEvent
TYPO3\CMS\Workspaces\Event\AfterCompiledCacheableDataForWorkspaceEvent
TYPO3\CMS\Workspaces\Event\AfterDataGeneratedForWorkspaceEvent
TYPO3\CMS\Workspaces\Event\GetVersionedDataEvent
TYPO3\CMS\Workspaces\Event\SortVersionedDataEvent

They replace the following "old" signals with a deprecation layer:

TYPO3\CMS\Backend\LoginProvider\Usern...