R1:812c41a18abd

Conditionally use `hg files` vs. `hg locate` depending on version of Mercurial

Summary:
In Mercurial 3.2 the `locate` command was deprecated in favor of `files` command. This change updates the DiffusionLowLevelMercurialPathsQuery command to conditionally use `locate` or `files` based on the version of Mercurial used.

Closes T7375

Test Plan:
My test/develop Phabricator instance is setup to run Mercurial 3.5.1.

The test procedure to verify valid file listings are being returned:
1. I navigated to `http…