Move LESS function definitions from DefaultSettings to LESSFunctions.php

Intermittent error in production from top-level lambda functions:
https://bugs.php.net/bug.php?id=52144

Change-Id: I9785a601fd5d57c9d8d84b90ee29eef61a6f2e77
(cherry picked from commit 11eb53abbc5ab3bf1ca5d60cf6adacd897860d3a)