Add regex flags parameter to python cudf strings split

[davidwendt]

Closes #3584

This depends on libcudf changes in PR #10128

This adds the regex parameter to the cudf strings split() function similar to the 1.4.0 Pandas one documented here.

The main difference is that the pat parameter will only be interpreted as regex if the pat string has more than 1 character and the regex parameter is set to True. This is to help with consistency and migration from the previous implementation.

The 1.3.x Pandas version does not have a regex parameter for split() but instead will try to interpret the intention of the pat parameter without it. This seems a bit dangerous since regex would be much slower for us here. Therefore, the regex parameter is required to be set to True in the cudf implementation in order to use the regex logic path.

Pandas does not support regex for its rsplit even though it has been documented and there is an issue here.

[codecov]

Codecov Report

Merging #10185 (65d906d) into branch-22.04 (a7d88cd) will increase coverage by 0.20%.
The diff coverage is n/a.

@@               Coverage Diff                @@
##           branch-22.04   #10185      +/-   ##
================================================
+ Coverage         10.42%   10.63%   +0.20%     
================================================
  Files               119      122       +3     
  Lines             20603    20954     +351     
================================================
+ Hits               2148     2228      +80     
- Misses            18455    18726     +271     

Impacted Files	Coverage Δ
python/cudf/cudf/_fuzz_testing/fuzzer.py	0.00% <ø> (ø)
python/cudf/cudf/_fuzz_testing/io.py	0.00% <ø> (ø)
python/cudf/cudf/_fuzz_testing/main.py	0.00% <ø> (ø)
python/cudf/cudf/_lib/strings/__init__.py	0.00% <ø> (ø)
python/cudf/cudf/_version.py	0.00% <ø> (ø)
python/cudf/cudf/comm/gpuarrow.py	0.00% <ø> (ø)
python/cudf/cudf/core/_base_index.py	0.00% <ø> (ø)
python/cudf/cudf/core/column/categorical.py	0.00% <ø> (ø)
python/cudf/cudf/core/column/column.py	0.00% <ø> (ø)
python/cudf/cudf/core/column/datetime.py	0.00% <ø> (ø)
... and 58 more

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[davidwendt]

@shwina I added support for regex in rsplit in this PR though it is not supported in Pandas (even in 1.4.0 as far as I can tell). I made it consistent with split which accepts a regex=True parameter (default to None). Let me know what you think. We can remove the rsplit regex support if you think that it would be confusing to have it here.

[davidwendt]

I added support for regex in rsplit in this PR though it is not supported in Pandas (even in 1.4.0 as far as I can tell). I made it consistent with split which accepts a regex=True parameter (default to None). Let me know what you think. We can remove the rsplit regex support if you think that it would be confusing to have it here.

@shwina Just wanted to check with you on this before merging.

[vyasr]

@gpucibot merge