Resolve default value expression

[jaapio]

php supports default values for method arguments, for a long time just scalar values were supported or const. That's why we are just using string values to represent the default values. But with introducing more complex expressions it makes sense to convert the method arguments into a object structure.

https://stitcher.io/blog/new-in-php-81#new-in-initializers-rfc

• [ ] const arguments should resove to class
• [ ] enum arguments should resolve to enum
• [ ] new initializer support in arguments.