Automate C++ include file grouping and ordering using clang-format

[Mark Harris]

Currently the C++ include files in the RAPIDS codebase are not consistently ordered and grouped.
Inconsistent ordering makes it harder to maintain the codebase, to understand the dependencies,
and to automate changes.

Using clang-format to automate the ordering and grouping of include files will not only add
consistent style, but it will ease automation of changes. For example, We are undertaking a
refactoring of RMM that will replace rmm::mr::device_memory_resource* with
rmm::device_async_resource-ref everywhere in RAPIDS (not just cuDF). This requires adding an
include to MANY files across multiple RAPIDS repos. Getting the location of this include correct
everywhere is very difficult without automatic grouping of headers.

I propose to use clang-format's IncludeCategories settings to automate the ordering and
grouping of include files in the C++ codebase consistently.

Proof-of-concept PRs have been created for RMM and cuDF:

• cuDF: rapidsai/cudf#15063
• RMM: rapidsai/rmm#1463

The ordering used for cuDF is given by the following settings.

IncludeBlocks: Regroup
IncludeCategories:
  - Regex:           '^"' # quoted includes
    Priority:        1
  - Regex:           '^<(benchmarks|tests)/' # benchmark includes
    Priority:        2
  - Regex:           '^<cudf_test/' # cuDF includes
    Priority:        3
  - Regex:           '^<cudf/' # cuDF includes
    Priority:        4
  - Regex:           '^<(nvtext|cudf_kafka)' # other libcudf includes
    Priority:        5
  - Regex:           '^<(cugraph|cuml|cuspatial|raft|kvikio)' # Other RAPIDS includes
    Priority:        6
  - Regex:           '^<rmm/' # RMM includes
    Priority:        7
  - Regex:           '^<(thrust|cub|cuda)/' # CCCL includes
    Priority:        8
  - Regex:           '^<(cooperative_groups|cuco|cuda.h|cuda_runtime|device_types|math_constants|nvtx3)' # CUDA includes
    Priority:        8
  - Regex:           '^<.*\..*' # other system includes (e.g. with a '.')
    Priority:        9
  - Regex:           '^<[^.]+' # STL includes (no '.')
    Priority:        10