Implement PartialOrd for TrieMap and TrieSet
Implement PartialOrd for SmallIntMap
Implement PartialOrd for Bitv and BitvSet
Implement Ord for TrieMap/TrieSet/SmallIntMap/Bitv/BitvSet
auto merge of #16038 : nham/rust/collections_partialord, r=alexcrichton

cc #15294