Add trie based greedy prefix construction

Dex savings for top 99 APKs:
Trie based: 4.82%
Greedy: 4.68%

Algorithm is to continuously pick the prefix that saves the most
bytes until there are no more savings.

Test: test-art-host
Bug: 77709234
Bug: 112311352

Change-Id: I686cfc35a1f17494294816493fb2a1107f3cd114