[10.x] Add ability to customize class resolution in event discovery

[bastien-phi]

I recently re-read a tweet by Dries saying "Most objects can be placed wherever you like in the app directory." https://twitter.com/driesvints/status/1526835414098534400?s=20

I develop my projects using the DDD structure defined by Brent in his blog. The main point here is the way namespaces are defined (https://stitcher.io/blog/laravel-beyond-crud-01-domain-oriented-laravel#on-the-topic-of-namespaces) :

{
    // …

    "autoload" : {
        "psr-4" : {
            "App\\" : "app/App/",
            "Domain\\" : "app/Domain/",
            "Support\\" : "app/Support/"
        }
    }
}

Everything goes well but event discovery does not work because file name to class name translation is not designed for this structure.

This PR adds the ability to customize the way the translation is done and unlocks event discovery in such DDD structures.