Refactor polymorphic allocator to use device_async_resource_ref

[harrism]

Description

Fixes #1540. Fixes #1453 by removing unused polymorphic_allocator::resource().

Checklist

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

[harrism]

/merge