Indirect instancing: Add support for potentially any shader derived from Unity Standard, currently enabled for all shaders in the Standard/ folder. Add support for MeshCull, RendererLOD and MeshLOD. Add editor scripts to enable GPU instancing and Read/Write on all assets. Use a nullable value for Color to allow future optimisations for non-coloured objects (most of them). Add the camera component from code, but only once. Rename instanding_id to instancing_handle. Rename IndirectInstancingManager and IndirectInstancing to IndirectInstancing and IndirectInstancingCamera respectively for clariy.