We supported CSS 'border-width', 'border-style' and 'border-color'
for HTML tables since 8a9bec35fb0c60a0e5990c1a12ffe6f39fdbf2d.
Now we also support the 'border' property, which is shorthand to
set all four borders' width, style and color.
Fixes: QTBUG-123167
Pick-to: 6.7 6.6
Change-Id: I5f29b94ab9facf412a9c230d554efb5c69368b6b
Reviewed-by: Shawn Rutledge <shawn.rutledge@qt.io>