This substantially redoes the logic by which bevel chooses, for
the middle segment when there are an odd number of segments,
which face to interpolate in, and which vertices to snap to which
edges before doing that interpolation. It changes the UV layouts
of a number of the regression tests, for the better.
An example, in the reference bug, is a cube with all seams, unwrapped
and then packed with some margin around them, now looks much
better in UV space when there are an odd number of segments.
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