Tokenizers - improve algorithm around exact matches.

Summary: Fixes T6102. Gets the from D10867 running in the tokenizer. This thing is pretty copy / pastey, but I guess that's okay?

Test Plan: looked at a project tokenizer and typed "project". since I have a million things with the word "project" in it, I was delighted to see the "project" project first in this project tokenizer.

Reviewers: epriestley

Reviewed By: epriestley

Subscribers: Korvin, epriestley

Maniphest Tasks: T6102

Differential Revision: https://secure.phabricator.com/D11305