winex11: Always forward SetCursor to the driver, and limit the frequency of updates on the driver side.

When we create a new font, we should store its height in a REAL field so
we don't have to round it. Further, when we calculate the width, we should
base the calculation on the metrics of a font at the height we will use, to
prevent rounding errors when the graphics transform will enlarge the font.

Like ca381b61, this was introduced by
f1ca14cb.