[php-src] Issue #21106: Missing trait is E_ERROR but missing extends/implements is Exception when autoloaded?

Issue: https://github.com/php/php-src/issues/21106
Author: kkmuffme

### Description

The following code:

```php
<?php
spl_autoload_register( function ( $class_name ) { 
    if ( $class_name === 'Foo' ) {
        require __DIR__ . '/foo.php';
    }
} );
try {
    class_exists( Foo::class );
} catch ( Throwable $e ) {
    echo 'catch' . PHP_EOL;
}
```

foo.php
```
class Foo {
    use Bar;
}
```

Resulted in this output:
```
Trait "Bar" not found
```

But I expected this output instead:
```
catch
```

Change foo.php to
```
class Foo extends Bar {}
```

and you will get the expected output. It's not consistent/illogical that traits behave differently in this regard?

### PHP Version

```plain
PHP 8.5
```

### Operating System

_No response_