Note: Applies to both UV Sphere Projection and UV Cylinder Projection.
Adds a new boolean option "Preserve Seams" to UV Sphere Projection.
With "Preserve Seams" active, the Sphere projection will do a
greedy flood fill over the 3D topology, stopping at 3D boundaries
and also stopping at edges where "Mark Seam" has been used in the
3D Viewport.
During the flood fill, each face is mapped using the spherical
projection and then adjusted along the U axis so the UV map is
continuous across the shared edge.
With careful seam placement, this allows for the creation of a
spiral-cut-orange-peel unwrap, where a sphere can be unwrapped
into a single long continuous strip, wrapping multiple times around
the object.
Finally, if the flood fill process creates multiple UV Islands,
they are spaced along the `U` axis to prevent overlaps.
Chris Blackbourn