Currently when exporting a subdivision surface (//Geometry / Export Subdivision Surface// enabled) the exporter uses a hard-coded BoundaryRule rule of 2 (CreaseAll, meaning hard corners). The subdivision surface modifier has an option for boundary smoothing mode so this patch propagates that information to the FBX exporter.

Example .fbx file with  this feature exported from modified Blender 2.93: https://github.com/bqqbarbhg/ufbx/blob/overhaul/data/blender_293x_subsurf_boundary_7400_binary.fbx

Reviewed By: mont29

Differential Revision: https://developer.blender.org/D12204