[libc++] Unspecified behavior randomization in libc++

This effort is dedicated to deflake the tests of the users which depend
on the unspecified behavior of algorithms and containers. This also
might help updating the sorting algorithm in libcxx which has the
quadratic worst case in the future or at least create a new one under
flag.

For detailed design, please see the design doc I provide in the patch.

Differential Revision: https://reviews.llvm.org/D96946

GitOrigin-RevId: a45d2287adf7942a26be02193731701e61eda7b4
13 files changed