Experimental option for the Reproject Strokes operator to project strokes on to
geometry, instead of only doing this in a planar (i.e. parallel to viewplane) way.
The current implementation is quite rough, and may need to be improved before it
is really ready for use. Potential issues:
* Loss of precision (i.e. stairstepping artifacts) from the 3D -> 2D -> 3D conversion
as we don't have float version of one of the projection funcs
* Jagged depth if there are gaps, since it will default back to the 3d-cursor plane
if no geometry was found (instead of doing some fancy interpolation scheme)
* I'm not sure if it's that useful for adapting GP strokes to deforming geometry yet...
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