Format of the mesh index buffer data.
Index buffer can either be 16 bit (supports up to 65536 vertices in a mesh), or 32 bit (supports up to 4 billion vertices).
Default index format is 16 bit, since that takes less memory and bandwidth.
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.
Changing indexFormat sets subMeshCount to one and clears the index buffer.
Refer to Mesh.MeshData.GetIndexData for an example.
Additional resources: IndexFormat, ModelImporter.indexFormat, SetIndices, SetTriangles, SetIndexBufferParams, SetIndexBufferData, MeshData.