DualView API documentation needs update

[dalg24]

To reflect kokkos/kokkos#6155

[Yaraslaut]

Also, there is no mension of these two functions in documentation, which are very handy
https://github.com/kokkos/kokkos/blob/1a3ea28f6e97b4c9dd2c8ceed53ad58ed5f94dfe/containers/src/Kokkos_DualView.hpp#L465-L469

  KOKKOS_INLINE_FUNCTION
  t_host view_host() const { return h_view; }


  KOKKOS_INLINE_FUNCTION
  t_dev view_device() const { return d_view; }

@ajpowelsnl do you have some time to update this ? otherwise I can try to make a PR