Reduce the number of TextAppearanceSpan objects for highlighting.

This CL removes unnecessary TextAppearanceSpan objects creation.

The hightlight text appearance of all suggestion items in popup window
are the same, so it is not make much sense to create TextAppearanceSpan
objects for each suggestion item.

This CL is a part of groundwork for Bug 15347319 and no user visible
change is intended with this CL.

Bug: 15347319
Change-Id: Ibad2e9842a76611a34187a3c942bae4ff7ea355f