[PHP][Symfony] Improve the implementation

[naelrashdeen]

Description

The current PHP Symfony server codegen is heavily based on the vanilla PHP codegen and does not really utilize the stuff Symfony brings to the table. This is especially true for input validation, serialization etc. It also lacks support for basic features such as:

• Proper deserialization of arrays in query, header, formData and path parameters
• Complete input validation that covers all cases
• Missing support for content negotiation through the Accept and Content-Type headers
• Support for response headers and response codes produced by the business logic