Subdivision shaders currently fail to compile using Metal as it doesn't recognize
packed_float3 as an internal data type. This PR includes packed_float3 as an
internal data type.
Without this `blender --debug-gpu-compile-shaders` will fail as it includes a namespace.
```
ERROR (gpu.shader): subdiv_normals_accumulate Compute Shader:
|
| source/blender/gpu/metal/mtl_shader_generator.mm:971:9: Error: no type named 'packed_float3' in 'MTLShaderComputeImpl'; did you mean simply 'packed_float3'?
|
| device MTLShaderComputeImpl::packed_float3* normals[[buffer(MTL_storage_buffer_base_index+4)]],
| ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
| packed_float3
|
| /System/Library/PrivateFrameworks/GPUCompiler.framework/Versions/32023/Libraries/lib/clang/32023.196/include/metal/metal_packed_vector:145:58: Note: 'packed_float3' declared here
|
| typedef __attribute__((__packed_vector_type__(3))) float packed_float3;
| ^
```
Pull Request: https://projects.blender.org/blender/blender/pulls/134925
b34bc67f67