[REVIEW] New stream-ordered suballocator resources (PTDS support)

[harrism]

This PR is bigger than originally planned, but it achieves quite a lot.

• Factors free lists into a base class defining the free_list abstract interface, and two implementations: fixed_size_free_list (for fixed-size block allocators) and coalescing_free_list (for coalescing pool allocators).
• Factors stream-ordered suballocation support into a new template abstract base-class stream_ordered_suballocator_memory_resource
• Reimplements fixed_size_memory_resource and pool_memory_resource in terms of the above classes.
• Both of these are now thread safe without using a thread_safe_resource_adapter.

TODO:

• Investigate whether fixed_multisize_memory_resource is thread safe without the adapter.
  Update: fixed_multisize_memory_resource and hybrid_memory_resource allocate/deallocate functions are thread safe as long as their upstream memory resources are thread safe. All currently available upstream resources in RMM are thread-safe after this PR. Therefore there is no longer a current need for thread_safe_resource_adapter.

[harrism]

Reviewers: I could use feedback on whether my use of move semantics is correct and consistent (and where I missed it). There are some other new (to me) C++ things in here that I used, like emplacing in a std::unordered_map using std::piecewise_construct and std::forward_as_tuple (In this case I needed to ensure the emplaced object's destructor is not called due to copying)

[GPUtester]

Please update the changelog in order to start CI tests.

View the gpuCI docs here.

[GPUtester]

Please update the changelog in order to start CI tests.

View the gpuCI docs here.

[harrism]

I'm seeing a big slowdown in the random_allocations benchmark. Investigating.

Fixed. But now I'm wondering if using CRTP rather than virtual functions would be faster. It's really too bad profiling CPU code is so hard.

Edit: the more I think about it CRTP makes a lot of sense for these classes (runtime polymorphism isn't really needed), but that should be a followup.

[harrism]

I removed the virtual inheritance in favor of CRTP in the stream_ordered_memory_resource base class.

[codereport]

This overall looks great. Love the use of algorithms and const :)

[jrhemstad]

The shared_ptr is a much nicer solution to the lifetime of the events.

[codereport]

Looks great!

[codereport]

❤️ 👍