[Workgroups] Add the missing Workgroups API.

The new Workgroups API is missing from the Xcode12 bindings. The framework allows to schedule threads in regular intervals before a deadline, this is useful for those applications that are working with Audio hardware. A talked from WWDC can be found [here](https://developer.apple.com/videos/play/wwdc2020/10224/).

The API is a C API can resides in the following headers:

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Of all the above headers, the is the umbrella one.