Add a "product name literal in pht()" linter

Summary:
Ref T13658. One challenge in forking Phabricator is product name references in user-visible strings, particularly in "pht()".

Add a linter to identify the use of product name literals in "pht()" text.

The linter could fix these automatically, but it looks like there are fewer than 200 across both Arcanist and Phabricator and some sampling suggests that many are probably clearer when rewritten into generic language anyway.

Test Plan: Ran linter, saw it pop out reasonable warnings.

Maniphest Tasks: T13658

Differential Revision: https://secure.phabricator.com/D21763