result::Element contains potentially redundant pointer information

[JakeHillion]

There are two fields in Element that are potentially redundant. We have pointer, an optional uintptr_t, and data which is a variant potentially containing a struct Pointer { uintptr_t p; };.

object-introspection/include/oi/result/Element.h

Lines 50 to 52 in 4c6f232

	std::optional<uintptr_t> pointer;
	std::variant<std::nullopt_t, Pointer, Scalar, std::string> data = {
	std::nullopt};

The question of which field is better depends on if we want to be able to store field data as well as pointer data. I suspect that we might for memory layout data along with value capture. In that case, we should probably remove the pointer field from the data variant and set pointer itself instead. If we never need both data and a pointer, we could drop the pointer field and always use the variant.