Replace Primitive with self

self should be preferred to the class name itself.

Author: roukmoute

tests/PHPUnit/Primitive.php

@@ -110,12 +110,12 @@ public function setString(string $string): void
         $this->string = $string;
     }
 
-    public function getPrimitive(): Primitive
+    public function getPrimitive(): self
     {
         return $this->primitive;
     }
 
-    public function setPrimitive(Primitive $primitive): void
+    public function setPrimitive(self $primitive): void
     {
         $this->primitive = $primitive;
     }