The block to invoke when progress is paused.
- iOS 7.0+
- macOS 10.9+
- Mac Catalyst 13.0+Beta
- tvOS 9.0+
- watchOS 2.0+
If the receiver is a child of another progress object, the
pausing block will be invoked when the parent is paused.
You are responsible for pausing any work associated with the progress object.
The pausing handler may be invoked on any queue. If you must do work on a specific queue, you should dispatch to that queue from within the pausing handler block.