Add missing OnPreferredSizeChanged call in RichTextView
Add equality operators to SizeConstraint
Size negotiation fixes

When caching the preferred size of a widget, also cache
the constraints that were used to get it. Only return
the cached size if the constraints match the cached ones

Hide scrollbars when the scroll policy is Never
[Mac] ScrollView fixes

Hide scrollbars when the scroll policy is Never.
Use the correct constraints when the width or height
of the scrollbar is fixed.