Add cuda_host_memory_resource

[pentschev]

Description

Add a new cuda_host_memory_resource backed by cudaMallocHost/cudaFreeHost that is similar to the existing pinned_host_memory_resource except it inherits from device_memory_resource instead of host_memory_resource, which has the advantage of being compatible with the rest of the RMM API, such as set_current_device_resource.

WARNING: Not ready to merge, this requires further discussion to determine whether the API is suitable for RMM. See also #1429.

Checklist

• I am familiar with the Contributing Guidelines.
• New or existing tests cover these changes.
• The documentation is up to date with these changes.