Breaking: #88687 - Configure extbase request handlers via PHP 

Description 

The configuration of extbase request handlers is no longer possible via typoscript. All typoscript concerning the configuration of request handlers needs to be converted to php, residing in EXT:Configuration/Extbase/RequestHandlers.php.

Impact 

Unless converted to php, the configuration in typoscript does no longer have any effect and therefore the registration of request handlers will no longer work.

Affected Installations 

All installations that configure request handlers via typoscript.

Migration 

Every extension that used typoscript for such configuration must provide a php configuration class called: EXT:Configuration/Extbase/RequestHandlers.php

The migration is best described by an example:

config.tx_extbase {
    mvc {
        requestHandlers {
            Vendor\Extension\Mvc\Web\FrontendRequestHandler = Vendor\Extension\Mvc\Web\FrontendRequestHandler
        }
    }
}

This configuration will look like this, defined in php:

<?php
declare(strict_types = 1);

return [
    \Vendor\Extension\Mvc\Web\FrontendRequestHandler::class,
];