Namespace usage could be more consistent and cleaner

[lsawade]

** Namespace usage could be more consistent **

E.g. This example from the Kokkos iterators.

namespace KE = Kokkos::Experimental;
using view_type = Kokkos::View<int*>;
view_type a("a", 15);

auto it = KE::begin(a);
// if dereferenced (within a proper execution space), can modify the content of `a`

auto itc = KE::cbegin(a);
// if dereferenced (within a proper execution space), can only read the content of `a`

Here it is clear that ...::begin and ...::cbegin are part of the Kokkos::Experimental section. Reminiscent of import numpy as np (I assume cpp did it first). Adds clarity for the reader.

It makes it much easier to learn the code without constantly right-clicking and asking for the definition/origin in your IDE.

Describe the solution you'd like

This is just basic refactoring.

Maybe a deliberate decision?

Please elaborate.