Rollup merge of #149477 - RalfJung:minimum-maximum, r=tgross35

float::maximum/minimum: make docs more streamlined

This does with `maximum`/`minimum` what rust-lang/rust#149475 did with `max`/`min`: first a self-contained description of the semantics, then comparing with other operations. It also makes the wording consistent with those other functions. Previously we had some of the semantics below the examples for some reason, and we repeated "If one of the arguments is NaN, then NaN is returned"; that has been streamlined as well.

r? `@tgross35`

Author: matthiaskrgr