Exempt some more puncutation characters from diff smoothing in prose diffs
Ref T7643. We intentionally smooth diffs, because an edit which changes "The cat ran past." to "The boar ran past." is easier to read if it looks like this:
The (- cat)(+ boar) ran past.
...than if it looks like this:
The (- c)(+ bo)a(-t)(+r) ran past.
However, this rule currently gives us slightly-too-large word diffs for "words" that contain some punctuation symbols, like ] and ). Include these as layout symbols to generate slightly better diffs.
Test Plan: Unit tests.
Reviewed By: chad
Maniphest Tasks: T7643
Differential Revision: https://secure.phabricator.com/D16853