metal: add all the files

src/host_shaders/metal_copy_to_lut_texture.metal

@@ -0,0 +1,9 @@
+#include <metal_stdlib>
+using namespace metal;
+
+constant ushort lutTextureWidth [[function_constant(0)]];
+
+// The copy is done in a vertex shader instead of a compute kernel, since dispatching compute would require ending the render pass
+vertex void vertexCopyToLutTexture(uint vid [[vertex_id]], texture2d<float, access::write> out [[texture(0)]], constant float2* data [[buffer(0)]], constant uint& arrayOffset [[buffer(1)]]) {
+    out.write(float4(data[vid], 0.0, 0.0), uint2(vid % lutTextureWidth, arrayOffset + vid / lutTextureWidth));
+}