Define expectations for exception messages

[lcobucci]

The tests which cover invalid data for annotations are allowing some mutations to exist:

x) src/Validator.php:33    [M] Throw_

--- Original
+++ New
@@ @@
     public function requiredScalar(string $attribute, string $type, $value) : void
     {
         if ($value === null) {
-            throw AnnotationException::requiredError($attribute, $this->annotation, $this->context, $type);
+            AnnotationException::requiredError($attribute, $this->annotation, $this->context, $type);
         }
         $this->verifyType($attribute, $type, $value);
     }

That happens because of an exception of the expected type is thrown by Validator#verifyType(). We should add the expected exception message and be able to remove these mutations.