Add support for phpstorm

[zmitic]

In PHPStorm, when you have code like $enum->equals() you don't have autocomplete of possible options.

That should be achievable with meta file: https://blog.jetbrains.com/phpstorm/2019/02/new-phpstorm-meta-php-features/

Now... I am not going to lie, I tried and failed:

// my enum class
/**
 * @method static Status INCOMPLETE()
 * @method static Status PENDING()
 * @method static Status FEEDBACK()
 * @method static Status OPTIONAL()
 * @method static Status APPROVED()
 */
class Status extends Enum
{
    private const INCOMPLETE = '(incomplete)';
    private const PENDING = '(pending)';
    private const FEEDBACK = '(feedback)';
    private const OPTIONAL = '(optional)';
    private const APPROVED = '(approved)';
}

and failed attempt of meta file (cache invalidated, just in case):

<?php

namespace PHPSTORM_META {

    registerArgumentsSet('profile_status_enum',
        \App\Doctrine\Enum\Status::PENDING(),
        \App\Doctrine\Enum\Status::APPROVED(),
        \App\Doctrine\Enum\Status::FEEDBACK(),
        \App\Doctrine\Enum\Status::INCOMPLETE(),
        \App\Doctrine\Enum\Status::OPTIONAL(),
    );

    expectedArguments(\App\Doctrine\Enum\Status::equals(), 0, argumentsSet('profile_status_enum'));
}

Used example was intentionally for real enum class, just to see if I can make it work.

I am honestly not sure if this is a bug in PHPStorm or more likely that I messed up but if someone has experience with this, it would be nice to have autocomplete by reading from values() method.

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The reason I created this issue is that if this library has meta file, PHPStorm will automatically pick it up. One composer update should be enough for end-users.