32 bit mesh index buffer format.
This format supports meshes with up to 4 billion vertices.
Note that GPU support for 32 bit indices is not guaranteed on all platforms; for example Android devices
with Mali-400 GPU do not support them. When using 32 bit indices on such a platform, a warning message will be
logged and mesh will not render.
See Also: Mesh.indexFormat, ModelImporter.indexFormat.