Symfony: Add support for #[MapRequestPayload] and #[MapQueryString] DTOs

[janedbal]

Problem

When a Symfony controller parameter uses #[MapRequestPayload] or #[MapQueryString], the framework's RequestPayloadValueResolver uses the serializer to create the DTO object. The DTO's constructor is called and its properties are populated — all invisible in user source code. This causes false positives where the DTO constructor, properties, and setter methods are reported as dead code.

The serializer behavior depends on the normalizer used. With the default ObjectNormalizer (registered at priority -1000 in Symfony's framework-bundle):

• Constructor is called with matching parameters
• Setter methods (setFoo()) are called via PropertyAccessor
• Public properties are written directly if no setter exists

Changes

• Detect #[MapRequestPayload] and #[MapQueryString] attributes on controller method parameters
• Resolve the parameter type to the DTO class
• Mark the DTO constructor as used
• Mark all declared properties as written
• Mark setter methods (set*) matching a property name as used
• Add ReflectionProvider dependency to SymfonyUsageProvider
• Add tests covering promoted constructor properties, query string DTOs, and setter-based DTOs

Co-Authored-By: Claude Code