Format of the mesh index buffer data.
Index buffer can either be 16 bit (supports up to 65535 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.
Note: the maximum possible vertex index (for example, 0xFFFF for a 16 bit index format) might not be usable. Some graphics APIs and GPUs skip rendering triangles with maximum vertex indices.
Additional resources: Mesh.indexFormat, ModelImporter.indexFormat, Mesh.SetIndices.