[CodeQuality] Skip non-constant constraint args in LoadValidatorMetadataToAttributeRector

[TomasVotruba]

An attribute argument must be a constant expression. When a constraint carried something evaluated at runtime — a closure, a method call, a variable — moving it to an attribute produced a file PHP cannot even parse.

Before:

public static function loadValidatorMetadata(ClassMetadata $metadata): void
{
    $metadata->addConstraint(new Callback(
        function (self $self, ExecutionContextInterface $context): void {
            $context->buildViolation('nope')
                ->atPath('slotName')
                ->addViolation();
        },
    ));

    $metadata->addPropertyConstraint('type', new Choice(choices: (new TypeList())->getChoices()));
}

Broken output, now fixed:

+#[\Symfony\Component\Validator\Constraints\Callback(function (self $self, ExecutionContextInterface $context): void {
+    $context->buildViolation('nope')
+        ->atPath('slotName')
+        ->addViolation();
+})]
 final class SomeClass
 {
+    #[\Symfony\Component\Validator\Constraints\Choice(choices: (new TypeList())->getChoices())]
     private $type;
-
-    public static function loadValidatorMetadata(ClassMetadata $metadata): void
-    {
-        ...
-    }
 }

Such constraints are now left in loadValidatorMetadata().

A new ConstantExpressionAnalyzer decides what may become an attribute argument. It whitelists what PHP accepts — scalars, constants, class constants, arrays, new (allowed in an attribute argument since PHP 8.1, so nested constraints like new Assert\All(new Assert\NotBlank()) keep working), unary and binary operations, ternary, array dim fetch — and rejects everything else.