Implement PartialEq/Eq/Clone/Hash/FromIterator/Extendable for SmallIntMap and Show/Clone for TrieMap and TrieSet
auto merge of #15963 : nham/rust/moar_15294, r=alexcrichton

Implements PartialEq/Eq/Clone/Hash/FromIterator/Extendable for SmallIntMap and Clone/Show for TrieMap/TrieSet. cc #15294