Three fixes:
* When smoothing a coord, the original position should be based off
the unsmoothed subdivision (i.e. the vertex coord rather than the
smoothed position in the shapekey)
* The normal of new vertices created by edge split must be updated
(used the same interpolation as pre-bmesh here)
* The vertices created inside the subdivided face should use the
subdivided coords from edges, so copy the shapekey coords back to
vertex coords after subdividing edges
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