This commit improves the export of enumerations (see https://wiki.php.net/rfc/enumerations). This change is backwards-compatible with PHP 8.0. Previously, enums would be exported as objects (which they are internally), for instance:
```
SebastianBergmann\Exporter\ExampleEnum Object #%d (
'name' => 'Value'
)"
```
This commit changes that behaviour and improves the export for both backed and non-backed enums:
Unit enum:
SebastianBergmann\Exporter\ExampleEnum Enum #%d (Value)
Backed enum:
SebastianBergmann\Exporter\ExampleBackedEnum Enum #%d (Value, 'value')
Marijn van Wezel