Part of a wider set of changes to migrate UV packing from
uv_parametrizer.cc to uvedit_islands.cc.
This allows UV packing improvements including margin calculation,
correctness fixes such as support for non-manifold geometry,
and new packing algorithms including speed and quality improvements.
See for example c2256bf7f7, T82637
This change migrates UV.unwrap and Live UV Unwrap.
Differential Revision: https://developer.blender.org/D16296
e3075f3cf7