[libc++] [test] Add "robust_re_difference_type.compile.pass.cpp" for all the algorithms.

Also, mark these tests as compile-only. They actually are safe to run — notice that
the code "runs" at constexpr-time in C++20, without error — because both of the
input ranges are entirely filled with nullptr, so no matter how you shuffle the
elements, they remain sorted and partitioned and heapified and everything.
But there's no real reason to run them at runtime, so let's just avoid the distraction.

Test cases that fail in trunk right now are commented out with `TODO FIXME`.

Differential Revision: https://reviews.llvm.org/D113906

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