New algorithm for drawing thin lines

New algorithm for drawing thin lines

Added a new QCosmeticStroker class for drawing thin
lines. The class can handle both aliased and antialiased
lines.

The code replaces all the midpoint line drawing algorithms in
the raster paintengine and gives correct subpixel positioning
for lines.

It gives around 30% to 50% speedup against the midpoint algorithm. If
we missed that fast path, the speedup is around between a factor of
6 to 8 for lines and aliased paths and 100 and 400 for antialiased
paths.

Reviewed-by: Kim
(cherry picked from commit 37c329a3e35fabc88fbcad824a69f37c671d2132)