Fix bounding rects of text items.

Ensure the rectangles are correctly positioned with right
and center aligned text, not just sized correctly. Also add
padding to the clip rects so the cursor and styled text aren't
clipped at the item boundaries.

Change-Id: I03ef140589154ebd49b600b0a4c4fbeff845c10f
Reviewed-by: Yann Bodson <yann.bodson@nokia.com>