enable the text layout's cache where it is seems to be missed

enable the text layout's cache where it is seems to be missed

e.g. in QStaticText, the data is used just to get the line's y-position
and re-calculates just after the loop to determine the bounding rect and to draw the text;

in QWidgetLineControl, the data re-calculated over and over while the result
is seems to remain the same; probably the caching is needed here too

Change-Id: I0f7eb291532f63eccb9c5f749daebb73ff90632f
Reviewed-by: Eskil Abrahamsen Blomfeldt <eskil.abrahamsen-blomfeldt@nokia.com>