Fix warning in access_traits_host example

[aprokop]

../examples/access_traits/example_host_access_traits.cpp(48): here

../src/details/ArborX_DetailsTreeConstruction.hpp(240): warning: calling a __host__ function("std::vector< ::ArborX::Point, ::std::allocator< ::ArborX::Point> > ::vector") from a __host__ __device__ function("") is not allowed

We never see them in CI due to #272. I'm not sure what's the best to fix it. Probably move away from using std::vector. Removing KOKKOS_FUNCTION would not work as Access::get is called from such a function.

[dalg24]

Well either we remove that example when CUDA is enabled or we keep on looking the other way.

[aprokop]

What is the thinking behind using std::vector in the example? With that, one is only able to construct the hierarchy, but not even query it as we need Kokkos::View for that.

[dalg24]

What is the thinking behind using std::vector in the example?

The motivation was to provide another example of access traits that does not require CUDA.

With that, one is only able to construct the hierarchy, but not even query it as we need Kokkos::View for that.

You need views for {offset, indices}, sure.