Instead of using a concept defined in the internal implementation, use a
definition of the simple_view ranges concept separately defined and
included in test code.
When we ship LLVM 16, <ranges> won't be considered experimental anymore.
We might as well do this sooner rather than later.
Differential Revision: https://reviews.llvm.org/D132151
Note that this class was called just `split_view` in the original One
Ranges Proposal and was renamed to `lazy_split_view` by
[P2210](https://wg21.link/p2210).
Co-authored-by: zoecarver <z.zoelec2@gmail.com>
Differential Revision: https://reviews.llvm.org/D107500
