Because of the linked list structure used for the ResourceList implementation, and the code that uses a while-loop to free elements in the list, memory segments allocated in a confined arena can currently not be scalar replaced.

While it doesn't seem possible to completely avoid allocations from escaping in this case (https://bugs.openjdk.org/browse/JDK-8345262) we can at least prevent the first allocation in a confined arena from escaping, by using a separate field to store just the first element in the list.