Pursuant to issue #25663, this commit adds the max and min functions to the Ord trait, enabling items that implement Ord to use UFCS (ex. 1.max(2)) instead of the longer std::cmp::max(1,2) format.
This change moves: 1. `libcoretest` into `libcore/tests` 2. `libcollectionstest` into `libcollections/tests` This is a follow-up to #39561.