Convert device_memory_resource* to device_async_resource_ref

[harrism]

Closes #4333

For reviewers:
Many of changes are simple textual replace of rmm::mr::device_memory_resource * with rmm::device_async_resource_ref.

However, I found that concurrent_unordered_map used in cuGraph is not up to date with the
latest changes from the version in libcudf, so I copied those over as well. This gets rid
of the hash_allocator.cuh, and uses rmm::mr::polymorphic_allocator instead of the custom
allocator previously used. This obviates the need to update any device_memory_resource* used
in the old custom allocator.

[ChuckHastings]

Thanks @harrism !

[ChuckHastings]

/merge