Provide some "preg_*" wrappers which raise exceptions on failure
Summary: Ref T13608. Ref T13100. Ref T13586. Properly checking "preg_match()" and similar calls for failure and raising useful exceptions is complicated and error-prone. Provide wrapper functions with an API that's more consistent with the rest of the codebase: matches are returned; and errors raise detailed exceptions.
Test Plan: See next change.
Differential Revision: https://secure.phabricator.com/D21561