Add filter over types in TSS_CASE_TPL

[jfalcou]

@jfalcou - can you implement filter? or what do you think?

[SadiinsoSnowfall]

// filter types with predicate
   template<template<typename> typename Pred, typename Type> struct filter
   {
     template<typename... Ls> static constexpr types<Ls...> tuple_to_types(const std::tuple<Ls...>&);
     template<typename T>
     static constexpr std::conditional_t<Pred<T>::value, std::tuple<T>, std::tuple<>> filter_type();

     template<typename... Ls> static constexpr auto filter_impl(types<Ls...>)
     {
       return tuple_to_types(std::tuple_cat(filter_type<Ls>()...));
     }
     using type = decltype(filter_impl(Type {}));
   };