Move rank scan implementations from scan_inclusive.cu to rank_scan.cu

[davidwendt]

This change was mainly to improve the compile time for reductions/scan/scan_inclusive.cu by refactoring out the rank-scan functions into a separate file rank.cu. Although the overall compile time improvement for scan_inclusive.cu is only 25%, the source code is better organized with this change. The code function has changed.

The detail inclusive_rank_scan and inclusive_dense_rank_scan declarations were moved from src/reductions/scan/scan.cuh to include/cudf/detail/scan.hpp and dispatching of the RANK and DENSE_RANK aggregation is done in scan.cpp instead of handled by scan_inclusive.cu and also scan_exclusive.cu (which just throws an exception anyway).

[codecov]

Codecov Report

Merging #9351 (9a7240a) into branch-21.12 (ab4bfaa) will decrease coverage by 0.04%.
The diff coverage is 2.07%.

❗ Current head 9a7240a differs from pull request most recent head 7c98115. Consider uploading reports for the commit 7c98115 to get more accurate results

@@               Coverage Diff                @@
##           branch-21.12    #9351      +/-   ##
================================================
- Coverage         10.79%   10.74%   -0.05%     
================================================
  Files               116      116              
  Lines             18869    19038     +169     
================================================
+ Hits               2036     2045       +9     
- Misses            16833    16993     +160     

Impacted Files	Coverage Δ
python/cudf/cudf/core/_base_index.py	0.00% <0.00%> (ø)
python/cudf/cudf/core/column/categorical.py	0.00% <0.00%> (ø)
python/cudf/cudf/core/column/column.py	0.00% <0.00%> (ø)
python/cudf/cudf/core/column/datetime.py	0.00% <0.00%> (ø)
python/cudf/cudf/core/column/numerical.py	0.00% <0.00%> (ø)
python/cudf/cudf/core/column/string.py	0.00% <0.00%> (ø)
python/cudf/cudf/core/column/timedelta.py	0.00% <0.00%> (ø)
python/cudf/cudf/core/dataframe.py	0.00% <0.00%> (ø)
python/cudf/cudf/core/frame.py	0.00% <0.00%> (ø)
python/cudf/cudf/core/index.py	0.00% <0.00%> (ø)
... and 19 more

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[harrism]

@gpucibot merge