P3133 R0 Fast first-factor finding function

[wg21bot]

P3133R0 Fast first-factor finding function (Chip Hogg)

[inbal2l]

Relates to P3045 (#1752)

[mattkretz]

Author requested that we only review this paper if a new revision lands.

why "needs-revision", from the author:

The tl;dr is that the paper isn't ready to discuss unless and until I
produce an R1 version. That version would need to be substantially fleshed
out, including:

• A reference implementation
• Benchmarks
• Deeper analysis of compiler iteration limits

Happily, we've learned that the utility is not blocking the critical path
for the units library after all! It turns out that every practical case we
have that exceeds compiler limits would be satisfied by a fast primality
checker, which I expect to be substantially easier to implement. (This
discovery also helps explain my reduced sense of urgency for this paper.)