[REQ] PHP Client/Server class property types

Created by: xvilo

Is your feature request related to a problem? Please describe.

Currently, PHP 7.4 has support for typed properties (see this RFC: https://wiki.php.net/rfc/typed_properties_v2). I think we should support this behind a feature flag.

Describe the solution you'd like

Add types to class properties, as we have them already as method arguments.

Additional context

This could be added for the following generators:

• clients
  • php (Guzzle)
• servers
  • PHP Laravel
  • PHP Lumen
  • PHP Slim
  • PHP Symfony
  • PHP Zend Expressive (with Path Handler)

I could create this functionality for the Symfony Server if this is wanted, for the others I would hope others could contribute to this.

As an example, the current model output for the PHP Symfony server is:

What it could become afterward: