Issue #2809237 by dmitryl, alexpott, iampuma, muschpusch, louisnagtegaal, twfahey, aburrows, Mike Lewis, nickmans, borisson_, jcnventura: Properly deprecate AllowedTagsXssTrait (cherry picked from commit 3791e77a71ccd14e61e1e2d10c9a1e306abee629)