Support assignment operator for layouts (and views)

[adayton1]

RAJA/util/TypedViewBase.hpp:481:23:

note: copy assignment operator of
ViewBase<int, care::host_device_ptr<int>, RAJA::detail::LayoutBase_impl<camp::int_seq<long, 0, 1>, int, -1>> is implicitly deleted because field m_layout has no copy assignment operator

layout_type const m_layout