Improve search stemmer performance for large inputs

Authored by epriestley on Sep 26 2017, 2:15 AM.

Description

Improve search stemmer performance for large inputs

Summary:
Ref T12974. See PHI87. As in D18647, we can improve the performance of some UTF8 operations here.

Instead of calling phutil_utf8_strtolower() on each token separately, call it once on the entire input up front. This has the same effect.

Test Plan:

Reviewers: amckinley

Reviewed By: amckinley

Maniphest Tasks: T12974

Differential Revision: https://secure.phabricator.com/D18648