Add _afterTransition method to Slideout to ensure same behavior regar… #9090

Job	Run time
ci / Code Quality / Rector / Rector	1m 42s
ci / Code Quality / PHPStan / PHPStan	2m 5s
ci / Code Quality / ECS / ECS	43s
ci / Code Quality / Prettier / Prettier	1m 3s
ci / Tests	1s
ci / Notify Slack	1s
	5m 35s

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