Make sure <figure> has proper dimensions

This commit brings back the sizing of the <figure> in MWBlockImageNode.
The figure must have proper size in CE otherwise 'center' and 'none'
alignments don't work, and the <figure> stretches across the entire
width of the screen.

Bug: 65836
Change-Id: Iefed466fce87f265fbd08908f1171867f9d1e1fe