ReadonlygenerationReadonlygeometryReadonlyslotOptional ReadonlytriangleTriangles left free before the mesh's in its batch's triangle buffer
(GpuBuildOptions.triangleLeading): an indexed scene that adopts the
buffer writes the mesh's header and side tables there. Default 0.
A mesh to build: its slot and version, and its geometry, read once when the build starts.