Replace boost conversion_traits with std::common_type

[Idclip]

Re-creating this so that we don't lose visibility on it. It currently cannot be merged due to https://github.com/AcademySoftwareFoundation/openvdb/issues/1700

[bpmckinnon]

One possible option given that std::numeric_limits is overridden is to try using std::numeric_limits<T>::is_specialized instead. https://en.cppreference.com/w/cpp/types/numeric_limits/is_specialized

[bpmckinnon]

I've verified that this is at least a potential option on my windows build... but I can't guarantee it will work in the build environment that is failing.

[apradhana]

As for the problem that Matthew raised in Issue 1700 , I have a fix that I included in the draft PR for supporting half grid. What's needed is adding a cwiseAdd specialization for Vec3<math::half> as shown here.

[bpmckinnon]

Has there been any update on the cwiseAdd function? Otherwise I can add the is_specialized change I proposed.