Revert the updates to .dashicons-plus (f132) in [33108] and instead introduce a new icon, .dashicons-plus-alt2 (f543).
props liljimmi, melchoyce, empireoflight.
see #30902.
git-svn-id: https://develop.svn.wordpress.org/trunk@33126 602fd350-edb4-49c9-b593-d223f7449a82