!!! FEATURE: Dispatcher psr overhaul

[mhsdesign]

To ease the implementation of a custom controller now use a direct pattern of f(ActionRequest) => PsrResponseInterface.
This is breaking if you implemented your own ControllerInterface or overwrote low level parts and methods of the ActionController.

class Dispatcher
{
    public function dispatch(ActionRequest $request): ResponseInterface;
}

interface ControllerInterface
{
    public function processRequest(ActionRequest $request): ResponseInterface;
}

Also, it's discouraged to manipulate $this->response in controllers (the ActionResponse is deprecated), although it's still supported in actions for now, please consider returning a new response instead.

Explanation of the legacy MVC response object.

Previously Flows MVC needed a single mutable response which was passed from dispatcher to controllers
and even further to the view and other places via the controller context: ControllerContext::getResponse().
This allowed to manipulate the response at every place.
With the dispatcher and controllers now directly returning a response, the mutability is no longer required.
Additionally, the abstraction offers naturally nothing, that cant be archived by the psr response,
as it directly translates to one: ActionResponse::buildHttpResponse()
So you can and should use the immutable psr {@see ResponseInterface} instead where-ever possible.
For backwards compatibility, each controller will might now manage an own instance of the action response
via $this->response AbstractController::$response and pass it along to places.
But this behaviour is deprecated!
Instead, you can directly return a PSR repose \GuzzleHttp\Psr7\Response from a controller:

public function myAction()
{
    return (new Response(status: 200, body: $output))
        ->withAddedHeader('X-My-Header', 'foo');
}

Further the ForwardException does not extend the StopActionException anymore, meaning a try catch must be adjusted.

This is the main PR and it contains

• !!! FEATURE: WIP Dispatcher and controller return ActionResponse (simpler controller pattern) #3232
• !!! TASK: Deprecate and replace ActionResponse in dispatcher #3294

Followup: #3301
Resolves: #3289

This change needs an accompanying adjustment to Neos to adjust the
PluginImplementation as well as Modules: neos/neos-development-collection#4738

Upgrade instructions

WIP Upgrade notes: #3232 (comment)

Review instructions

Checklist

• Code follows the PSR-2 coding style
• Tests have been created, run and adjusted as needed
• The PR is created against the lowest maintained branch
• Reviewer - PR Title is brief but complete and starts with FEATURE|TASK|BUGFIX
• Reviewer - The first section explains the change briefly for change-logs
• Reviewer - Breaking Changes are marked with !!! and have upgrade-instructions

[mhsdesign]

will be fixed via #3301

[mficzel]

I like this by reading and it makes a lots of sense. Would lite to test this before finally approving. Will take some tome. Maybe count this as +0.5 in the meantime