The grease pencil draw tool would still do a lot of smoothing
even if the active smoothing factor was set to 0.0.
This was because the screen space coordinates were always pre-blurred
before being passed to the curve fitting. Even if the curve fitting
outputs a line that fits the input exactly, it would still use the pre
smoothed coordinates.
The fix makes sure to use the smoothing factor in the influence
of the pre-blur. This way, no pre-blur is used when the factor is 0
and the lines will be smoothed much less.
Note that we always do some smoothing to avoid artifacts such
as pixel-grid-aligned lines etc.
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