Issue #3405800 by alexpott, phenaproxima, Wim Leers, bircher, larowlan: Config collections do not trigger configuration events consistently

Issue #3055198 by catch, longwave, mikelutz, alexpott: [Symfony 5] Symfony/Component/EventDispatcher/Event is deprecated in Symfony 4.3 use Symfony/Contracts/EventDispatcher/Event instead

Issue #2665992 by alexpott, klausi, heykarthikwithu, xjm, tstoeckler: @file is not required for classes, interfaces and traits