Extract magic string to named constant DYNAMIC_PROPERTY_NAME

Address review feedback: the magic string '__phpstan_dynamic_property'
is now a private constant with a docblock explaining its purpose.
It serves as a representative property name for dynamic property access
resolution ($obj->{$expr}), allowing PropertiesClassReflectionExtensions
that accept any property name to return the correct type.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: phpstan-bot

src/Analyser/ExprHandler/PropertyFetchHandler.php

@@ -33,6 +33,14 @@
 final class PropertyFetchHandler implements ExprHandler
 {
 
+	/**
+	 * Representative property name used when resolving dynamic property access ($obj->{$expr}).
+	 * The actual name doesn't matter — it just needs to be non-empty so that
+	 * PropertiesClassReflectionExtensions (e.g. SimpleXMLElement) that accept
+	 * any property name can return the correct type.
+	 */
+	private const DYNAMIC_PROPERTY_NAME = '__phpstan_dynamic_property';
+
 	public function __construct(
 		private PhpVersion $phpVersion,
 		private PropertyReflectionFinder $propertyReflectionFinder,
@@ -132,7 +140,7 @@ public function resolveType(MutatingScope $scope, Expr $expr): Type
 
 		if ($nameType->isString()->yes()) {
 			$fetchedOnType = $scope->getType($expr->var);
-			$returnType = $this->propertyFetchType($scope, $fetchedOnType, '__phpstan_dynamic_property', $expr);
+			$returnType = $this->propertyFetchType($scope, $fetchedOnType, self::DYNAMIC_PROPERTY_NAME, $expr);
 			if ($returnType !== null) {
 				return NullsafeShortCircuitingHelper::getType($scope, $expr->var, $returnType);
 			}