Turn off universal box-sizing in alpha

This has apparently been causing issues for VisualEditor
Thus in alpha, to allow us to explore any breakage,
restrict it to views except VisualEditor
(I dislike the class name but I imagine this will only be temporary
whilst we work out what if anything actually needs this)
Bug: T85068
Bug: T86366
Change-Id: Iba498e31dece2e03351c8fd8ba04b90be128bd16