UPGRADE FROM 5.x to 6.0
=======================
EventDispatcher
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* Removed `LegacyEventDispatcherProxy`. Use the event dispatcher without the proxy.
FrameworkBundle
* `MicroKernelTrait::configureRoutes()` is now always called with a `RoutingConfigurator`
HttpFoundation
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* Removed `Response::create()`, `JsonResponse::create()`,
`RedirectResponse::create()`, and `StreamedResponse::create()` methods (use
`__construct()` instead)
Routing
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* Removed `RouteCollectionBuilder`.