lib/msun: Added fmaximum and fminimum family. Tests and man page

Starting from the existing fmax{,f,l} functions I've added the fmaximum
family, which handles NaN according to the newest standard (p

lib/msun: Added fmaximum and fminimum family. Tests and man page

Starting from the existing fmax{,f,l} functions I've added the fmaximum
family, which handles NaN according to the newest standard (propagating
it).

This commit is a PoC for GSoC 2026.

Reviewed by: fuz, kargl
MFC after: 1 month
Differential Revision: https://reviews.freebsd.org/D55834

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