[css-text-4] decimal alignment in tables image for Issue 18

Attached is an image two possible ways of handling the alignment of the
alignment character across different font weights (see issue 18 [1] in
spec). The most common use case is bold vs regular text in the table column.

The top image shows the alignment characters aligned at the character
origin.

The bottom shows the alignment characters centered.

The font is Adobe Caslon; bold text (gray) in back; the roman in front.

Dave



[1] https://drafts.csswg.org/css-text-4/#character-alignment