[5.3] Guess policy method from class name

[alepeino]

Very minor improvement for handling the case of Actions That Don't Require Models so that the policy and the ability to authorize can be guessed from a class name.

Example:

public function create()
{
    $this->authorize(Post::class);

    // ...
}

[JoostK]

Can you remove the additional parenthesis?

[JosephSilber]

This originally wasn't added because it's a little brittle. People use all sorts of crazy ability names, and it may overlap with an existing class name.

Maybe we indeed shouldn't care, and just cater to the 99%. However, we stick to that rule when the 1% has a (less elegant) way to achieve their desired result. In this case however, if you have an ability whose name matches an existing class, there'd be no recourse.

Maybe instead of checking for class_exists we should check if it looks like a class name? Since a method on the ability cannot have a slash in it, there's no way this would break for anyone.