nvk: Manually offset for array layers in copy/blit

nvk: Manually offset for array layers in copy/blit

The more I start at the hardware the more convinced I become that arrays
and 3D are not the same thing.  I'm sure they're similar enough in
certain circumstances but they don't appear to be in the way they're
treated in the 2D hardware, especially when miplevels are involved.
Instead of trying to use the 2D engine's depth/slice logic, offset
manually.  We have to emit a copy command for each slice anyway so
making the GPU do those calculations doesn't really gain us anything.

Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/24326>