Rollup merge of #72836 - poliorcetics:std-time-os-specificities, r=shepmaster
Rollup merge of #72836 - poliorcetics:std-time-os-specificities, r=shepmaster

Complete the std::time documentation to warn about the inconsistencies between OS

Fixes #48980.

I put the new documentation in `src/libstd/time.rs` at the module-level because it affects all types, even the one that are not directly system dependents if they are used with affected types, but there may be a better place for it.

graydon/rust,graydon/rust,aidancully/rust,graydon/rust,aidancully/rust,graydon/rust,aidancully/rust,graydon/rust,aidancully/rust,aidancully/rust,aidancully/rust,graydon/rust