[REVIEW] Moving cuML prims to RAFT

[divyegala]

This PR moves cuml prims to RAFT that will break the circular dependency between libcuml and libcumlprims. The changes made in these files are almost exactly the same as those mirrored by cuML, with only the header paths updated to reflect how raft does it:

1. Like #include <common/cudart_utils.h> became #include <raft/cudart_utils.h>
2. "#include "test_utils.h" became "../test_utils.h" (Our prims gtests are all in the same, root level tests/prims folder but I took the liberty of dividing it more as tests/linalg, tests/stats, etc.)

In any case, these changes will not affect when we finally delete prims from cuML. Only thing we would need to do there is also update the include path for these prims (files moved), as they are already in the correct formatting and namespaces.

[GPUtester]

Please update the changelog in order to start CI tests.

View the gpuCI docs here.

[JohnZed]

We discussed offline that the build changes are new, but can you clarify the other files - are they all exact copies of the recently-updated cuml versions? Or are there additional changes?

[divyegala]

@JohnZed updated the description of the PR to clarify

[raydouglass]

rerun tests

[mike-wendt]

Doesn't look like we're needed for code review, removing @rapidsai/ops-codeowners; add us back if necessary. Thanks!

[JohnZed]

Looks straightforward to me! Thanks for making the move.

[divyegala]

@JohnZed added the leftover prims, as I mentioned on the call. Reference cuml PR is rapidsai/cuml#3044

[JohnZed]

GIven approvals from both ML and graph, I'll go ahead and merge. Excellent stuff, @divyegala !