Add experimental ManagedArrayPointer

[adayton1]

ManagedArrayPointer is the experimental replacement for ManagedArray. All the logic for handling various memory types is delegated to a ManagerType template parameter.

This class provides a uniform interface for working with different types of memory across multiple backends. It has pointer semantics, meaning that copies are shallow, which allows this object to be passed by value to a CUDA or HIP kernel. When copy constructed, it queries the array manager to update the cached size and pointer from the array manager. The array must be explicitly freed from only one of the shallow copies.

[robinson96]

LGTM

[rhornung67]

Is there a way for a user to check whether the data referenced by a ManagedArrayPointer has been freed; e.g., by another pointer object pointing to the same data? If not, it may be worth considering. I can see how that would be useful.

[adayton1]

Not without a lot of extra tracking. My plan was to add another class called ManagedArraySharedPointer that would act like std::shared_ptr and avoid the need to explicitly free.

[rhornung67]

Yeah. I figured that would be the case. You solution sounds like it should do the trick.

[rhornung67]

Looks good to me. One comment to consider.

Also, you may want to rework the copyright statements in the files like I did in RAJA. Then, updating the copyright year only requires touching 2 files instead of all of them, which kinda pollutes the commit history of each file.

Here's the change: llnl/RAJA#1976