Move thrust::is_trivially_relocatable to libcu++

[bernhardmgruber]

I am of the opinion that we should be moving this trait into libcu++ and derive it from is_trivially_copyable as a default and then users to specialize it.

Note that the definition from the paper is much more complex and would require compiler support

Originally posted by @miscco in #2010 (comment)

From offline discussion: I good place for the trait would by in <cuda/std/type_traits> but inside namespace cuda.