…lock/instant/duration (#165)

* Remove the disable of availability and mark methods as available to clock/instant/duration

* Rework availability to be more permissive for tests

* Use hand coded values instead of defines (only available via Darwin versions of Dispatch)

* Adjust additional test availability

* Correct debounce test availability guard

* Update build instructions to indicate Xcode requirements

* Ensure the clock property of the validation diagram is only available for targets that can support it