Use type declaration in argument 3 of php_user_filter::filter()

[phansys]

No description provided.

[Girgias]

We cannot do this, as internal functions must treat any reference parameter as mixed with ZPP and do manual type checking. So this change just as is is incorrect.

[kocsismate]

Yeah, I'm closing the PR because it's not possible to declare these parameters indeed as Gine said, since no parameter type check is performed at the start of the function. Adding support for In/out parameters would be needed in order to be able to declare the type of such parameters.