File inclusion - check for constant defined in the current file

## What problem would the enhancement address for VIP?

The frequency with which "Warning: File inclusion using custom constant (`PREFIX_PATH`). Probably needs manual inspection (WordPressVIPMinimum.Files.IncludingFile.UsingCustomConstant)." shows up just below a line that matches the pattern is high.

Perhaps we can reduce this noise.

## Describe the solution you'd like

See if we can improve the sniff, to see if the constant has been defined in the current file, and if so, skip the violation.

## What code should be reported as a violation?

```php
require PREFIX_PATH_UNDEFINED_IN_THIS_FILE . '/...';
```

## What code should *not* be reported as a violation?

```php
define( 'PREFIX_PATH_DEFINED_IN_THIS_FILE', '...' );
...other code...
require PREFIX_PATH_DEFINED_IN_THIS_FILE . '/...';
```

Commencez par localiser le sniff qui émet WordPressVIPMinimum.Files.IncludingFile.UsingCustomConstant et examinez comment il détecte les constantes dans les expressions d’inclusion de fichiers. Ajoutez une couverture pour l’exemple de constante non définie et pour la constante définie plus tôt dans le même fichier ; le travail est terminé lorsque seul le cas de la constante non définie est signalé.

Rédigé par le modèle d'indexation à partir du texte de l'issue.