Fix a number of issues that caused polygons to not always be drawn
fully connected.
Ensures the original lastPixel is set when drawing closed polygons,
ensure we don't round away from the original starting point, and add
handling of edges that need to be rounded half a pixel sideways to line
up with endpoints.
Task-number: QTBUG-27053
Change-Id: Ib51ee5623a629996af51a0967096383f04e91e2f
Reviewed-by: Eirik Aavitsland <eirik.aavitsland@qt.io>
d866617ea6