Fixing height of tool link

The default height in ooui-js is 1.5 em. For mobile it needs to be
3 em so that it takes up the entire height of the toolbar (and more
than just the top half of the button is clickable). This matches
the 3 em height override for oo-ui-tool.

Change-Id: I03a139099f09dfb992ce692887d73470c18f86a0
Merge "Fixing height of tool link"