Calculate a tangent per loop, apply the transformation in multiple
spaces and accumulate the result weighting by the loop-angle.
Note that previously only the tangents Z axis (normal)
was properly accumulated, the X and Y axes only contained the values
from a single loop (the last one written to), meaning only two edges
contributed to the result. Now the transformation from all loops are
taken into account.
In practice the difference between both methods is minimal,
only for more extreme bending it can be noticed which is often when the
previous method didn't work as well.
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