Add Alembic scene exporter

The IO/Alembic module now provides a new scene exporter for the Alembic file format. This format is used for dynamic scene and complex geometry exchange for 3D modeling packages.

The class vtkAlembicExporter exports the current visible scene to an “.abc” file. This includes all visible polygonal geometry, with vertex colors and texture coordinates. If a colormap has been applied, a texture containing the colormap is also saved as a “.png” file. The camera position and orientation is also exported. Blender 3.6 imports these scene files, and other modeling packages like 3D Studio Max and Maya also have Alembic importers.