objc2-audio-toolbox is missing the Workgroup API

[ilmai]

As it says in the title. All of this is missing right now: https://developer.apple.com/documentation/audiotoolbox/workgroup-management

[madsmtm]

It's missing because we're missing an API for os_workgroup_t. Not entirely sure in which crate such an API makes sense to live? Maybe libc? E.g. dispatch_workloop_set_os_workgroup also needs access to it.

[ilmai]

os_workgroup_t is defined as a pointer to OS_os_workgroup which is an Obj-C object if I'm reading this right, so it doesn't sound like it belong to libc? Maybe there should be a new objc2 crate for the os "framework" (as it's defined in documentation though I don't think it's a real framework)? Not sure tbh what would make the most sense, I'm not too familiar with MacOS development myself.

[madsmtm]

It is also an Objective-C object on modern macOS, but primarily it's a reference-counted object (whose reference-count is controlled by os_retain and os_release).

[madsmtm]

Looking at the linking, it doesn't seem like a libos.dylib exists, the symbols are exported by libdispatch.dylib, so maybe it makes sense to define the symbols in dispatch2 too? Unsure, but probably what I'm leaning towards.