Iterate over the object's members and call a filter callable to decide what
to do with the current key/value. A filter returns one of the `FilterResult`
values. A container type is an associative or a sequence container of pairs
(key, value).
Refactor `MapFilter()` and `Map()` to use `FilteredObject()`. Moreover,
for C++ >= 17 implementation is more optimized depending on the given filter
object type and capable of detecting and properly calling the filter callable
using 1 or 3 arguments, up to totally eliminate any checking (even dummy)
in the generated code.
Supported container types, used to append key/value items, aren't limited to
`std::map` only and can be any associative container or a sequenced one with
pairs of key/value as elements.
0c17cc9ef5