In addition to being more consistent with our approach for helpers, this
solves an actual issue where <cmath> was using numeric_limits but never
including the <limits> header directly. In a normal setup, this is not
an issue because the <math.h> header included by <cmath> does include
<limits>. However, I did stumble upon some code where that didn't work,
most likely because they were placing their own <math.h> header in front
of ours. I didn't bother investigating further.
Differential Revision: https://reviews.llvm.org/D115282
Actually there's one functional change here, which is that users can
no longer depend on <random> to include all of C++20 <concepts>. That
inclusion is so new that we believe nobody should be depending on it
yet, even in the presence of Hyrum's Law. We keep the includes of <vector>,
<algorithm>, etc., so as not to break pre-C++20 Hyrum's Law users.
Differential Revision: https://reviews.llvm.org/D114281
Arthur O'Dwyer