[FIX] layout/Splitter: Correct focus outline in IE

IE seems to have problems rendering outline correctly and also
does not seem to support outline-offset. This fix creates a pseudo-
element in IE over the splitter bar that has a border in the style
of the focus outline.

Change-Id: I769b7d7765778c7f74bfeffca715c46ce56f280e
Merge "[FIX] layout/Splitter: Correct focus outline in IE"