feat: add class_alias to add alias to original class name

[kenng]

This pull request adds support for class_alias to Tinker's configuration.

Motivation:
We created a model App\Models\Event, which conflicts with the events facade. As a result, instead of the Event model class being aliased, the events facade was aliased.

This solution allows users to map the conflicting class name to another class. For example, in config/tinker.php.

<?php

return [
    'class_alias' => [
        'AppEvent' => App\Models\Event::class,
    ],
];

[taylorotwell]

Thanks for your pull request to Laravel!

Unfortunately, I'm going to delay merging this code for now. To preserve our ability to adequately maintain the framework, we need to be very careful regarding the amount of code we include.

If possible, please consider releasing your code as a package so that the community can still take advantage of your contributions!

If you feel absolutely certain that this code corrects a bug in the framework, please "@" mention me in a follow-up comment with further explanation so that GitHub will send me a notification of your response.