Inconsistency about ::class and literal strings

### Description

This doesn't work (https://3v4l.org/MM1pJ):

```php
<?php

$foo = 'Foo';
var_dump($foo::class);
```

But this does (https://3v4l.org/Rb3oU)

```php
<?php

var_dump('Foo'::class);
```

Is this intentional? I'd say both or neither should be supported.

### PHP Version

Irrelevant

### Operating System

N/A