Metal Argument Buffer support

[cpredmann]

Metal Argument Buffers are referred to in the documentation, in reference to Parameter Blocks. However, no combination of .metal shader generation with ParameterBlocks seems to output the [[id(x)]] attributes on the output struct. And the kernel argument is a pointer to the ParameterBlock struct rather than a reference. Is there something undocumented that I'm missing, or is this functionality not complete?

[cpredmann]

Ah, it's just non-standard format, but you can still bind ParameterBlock as argument buffer...