[5.8] Fix guessed policy names when using Gate::forUser

[erikgaal]

Overview

When using the Gate facade to create a new instance for a specific user with forUser the guessPolicyNameUsingCallback is not passed on to the new instance. This results in the policies no policies being loaded when using just the policy name guesser.

Reproduction

Gate::guessPolicyNamesUsing(function ($class) {
    return 'foo';
});

dump(app(Gate::class));
// #guessPolicyNamesUsingCallback: Closure($class) {#371

dump(app(Gate::class)->forUser($user));
// #guessPolicyNamesUsingCallback: null

Proposed Solution

Add the guessPolicyNameUsingCallback nullable argument to the constructor and pass it in the forUser method.

[erikgaal]

This probably needs a test so it won't break again.

[TBlindaruk]

@erikgaal #27757 I have created issue for the test