Function phpdoc_replace_genericTs_with_reified

* When we have a generic function and an instantiation T=User, replace all T's inside a type hint. * We also handle @return here, that can ref to a field T::fieldName, replacing it after T is instantiated. * (note, that we don't allow ClassName::fieldName anywhere but in generics; if it's written, it will fail on type inferring) */