Resolved Documentation/API Accessibility: NativeContainerAttribute example uses internal API in documentation

The example in the NativeContainerAttribute documentation on how to create safe native containers without using DisposeSentinel uses the functions CollectionHelper.CreateSafetyHandle and CollectionHelper.DisposeSafetyHandle. These functions are marked internal so they aren't accessible to us. It's not really possible to copy the code either, as CollectionHelper.DisposeSafetyHandle accesses the internal (I assume) field of AtomicSafetyHandle. It would be nice if these functions could be made public so we could use them the way the NativeContainerAttribute example uses them.

In general, it would be nice if more of the CollectionHelper functions could be made public. A lot of them are convenience functions that it would be nice not to have to duplicate, such as AssumePositive, CheckIndexInRange, ShouldDeallocate, etc. Particularly for the functions that are conditionally compiled away if ENABLE_UNITY_COLLECTIONS_CHECKS isn't defined.