Support NonZero[UI]size when [ui]size is supported
This closes an orthogonality gap: While NonZeroXxx has been supported, and usize/isize have been supported on 32 and 64 bit platforms, NonZeroUsize/NonZeroIsize have not been supported; this closes the gap.
From my point of view there is no urgency to do a release on this (whereas the latest ones with the position are highly appreciated): The workaround of going Into and unwrapping works well enough.