Implement {async_}resource_ref

[miscco]

This implements the NVIDIA internal proposal for a any_resource_ref abstraction that facilitates the handling of memory allocations on host and device side.

To facilitate adoption the proposal is backported to C++14 / C++17 through a concept emulation designed by @ericniebler. Unfortunately, C++11 is too far a stretch due to missing support for constexpr variables.

Currently only plain any_resource_ref resource is implemented, as async_resource_ref is more or less a straightforward extension.

Things still to do:

• Implement async_resource_ref
• Implement equality_comparable concept
• Write some documentation

[jrhemstad]

fyi @miscco we'll likely want to steal some things from #158, like stream_view (though probably rename to stream_ref) and maybe some of the exception stuff. It also has quite a few tests that could be helpful for showing what kind of tests we want here.

[miscco]

NOTE to reviewers:

I have pushed the concept emulation into its own branch and targeted this PR to that branch. Consequentlly, we can review only the memory_resource part of the PR. Before merging we would need to change the target branch back to main

[harrism]

I'm bothered that this was merged without finishing the documentation checkbox. At least a new issue should be opened when that happens.