Visible spans changes only invalidate the affected text sub display lists

When a span with a visible influence on the text is modified, we only
need to invalidate the text sub display lists that overlap this span.

This is especially useful when typing and the composing span (an underline
span) gets updated after each key stroke.

Change-Id: Ib2af3219c41eb79ec5d0a2eee317aca8c4efdef9