R1:7bd2994c2e21

Improve atomizing of PHP `@return` annotation

Summary: Fixes T6890. This doesn't feel like a perfect solution, but I can't think of any cases in which this will produce the wrong result either.

Test Plan: Ran `./bin/diviner generate` and checked the generated documentation for `PhabricatorCommonPasswords::loadWordlist()`. The return type was corrected shown as `map<string, bool>`.

Reviewers: #blessed_reviewers, epriestley

Reviewed By: #blessed_reviewers, epriestley

Subscribers: Korvin, epriestley…