Add new package GPUToolsCapture under vendor:darwin/Metal

[antinaho]

Apple's documented pattern for programmatic GPU capture, Capturing a Metal workload programmatically, assumes the Metal device is already wrapped with the capture layer.

Currently MTLCaptureManager.startCaptureWithDescriptor:error: returns Capture layer is not inserted. error while other MTLCaptureManager.startCaptureWith* dont emit the recorded .GPUTraceDocument when ending the recording.

Xcode injects this layer automatically when launching a Metal app. Standalone Odin programs have no way to do this currently. In effect, MTLCaptureManager and MTLCaptureDescriptor are unusable from Odin today.

Proposal:
Add an extra package under Metal or extend the current Metal package to expose a way to wrap the MTLDevice. Change would be extra ~10 lines.

import MTL "vendor:darwin/Metal"

@(extra_linker_flags="-F/System/Library/PrivateFrameworks")
foreign import "system:GPUToolsCapture.framework"

@(default_calling_convention="c")
@(link_prefix="DYMTL")
foreign GPUToolsCapture {
	WrapDeviceWithDebugLayer :: proc "c" (device: ^MTL.Device) -> ^MTL.Device ---
}

[antisaling]

well you can do this on your application no? I mean it would be better to have a shared thing for everyone to use, but I don't get your claim that "Standalone Odin programs have no way to do this currently"

either way, feel free to open a PR, I'll be glad to test and review