(Apologies in advance if I have completely messed up the process, it's my first time. I did read all of the "Contributing" guidelines so I tried to do it right!)
Add a 'text.trailing-whitespace-non-empty-only' option to ArcanistTextLinter to allow for the trailing whitespace check to only apply to non-empty lines. This makes it cooperate better with editors like Xcode that maintain the indent level on empty lines.
This intends to satisfy the feature request logged at https://discourse.phabricator-community.org/t/feature-request-trailing-whitespace-only-on-non-empty-lines/806/1 (I couldn't figure out how to create a Feature Request task on this Phabricator instance.)
