Use typed properties for ValidatorChain & FilterChain in Input

[pascalheidmann]

Q	A
Documentation	no
Bugfix	no
BC Break	yes
New Feature	no
RFC	no
QA	no

Description

This PR will add property types for base Input class for $validatorChain and $filterChain properties. As those could be accessed in derived classes directly and not via their appropriate getters/setters this is breaking. The purpose of this PR is to remove confusion for phpstan (not sure about psalm) as it will detect a nullable property as technically it is null as long it isn't set or initialized via getValidatorChain()/getFilterChain().

[Ocramius]

This can't really be done, as it is a BC break for child classes.