Implement shift_left and shift_right

[dkolsen-pgi]

shift_left and shift_right are two new standard algorithms with parallel overloads that were added in C++20.

https://en.cppreference.com/w/cpp/algorithm/shift

In the interest of completeness, it would be nice if Thrust implemented these two new algorithms.

[miscco]

I will give this a try to familiarize a bit better with thrust.

Note to past self: push branches before handing back a machine