String support for jcudf row to cudf column conversion

[hyperbolic2346]

This PR adds support for string column creation from jcudf row data. It leverages the fixed-width data copy to convert the offsets and lengths stored inside the fixed-width data section and then uses that information to copy the string data itself from the jcudf row format into the cudf column.

closes #10286

[codecov]

Codecov Report

Merging #10871 (546b4b4) into branch-22.06 (6352b4e) will increase coverage by 0.02%.
The diff coverage is 100.00%.

@@               Coverage Diff                @@
##           branch-22.06   #10871      +/-   ##
================================================
+ Coverage         86.29%   86.32%   +0.02%     
================================================
  Files               144      144              
  Lines             22656    22668      +12     
================================================
+ Hits              19552    19569      +17     
+ Misses             3104     3099       -5     

Impacted Files	Coverage Δ
python/cudf/cudf/core/_base_index.py	85.71% <ø> (ø)
python/cudf/cudf/core/frame.py	93.41% <ø> (ø)
python/cudf/cudf/core/groupby/groupby.py	91.79% <ø> (+0.22%)	⬆️
python/cudf/cudf/core/index.py	92.06% <ø> (ø)
python/cudf/cudf/core/indexed_frame.py	91.70% <ø> (ø)
python/cudf/cudf/core/series.py	95.17% <ø> (ø)
python/cudf/cudf/core/column/string.py	88.78% <100.00%> (+0.12%)	⬆️
python/dask_cudf/dask_cudf/groupby.py	97.42% <100.00%> (+<0.01%)	⬆️
python/dask_cudf/dask_cudf/tests/test_groupby.py	100.00% <100.00%> (ø)
python/cudf/cudf/utils/ioutils.py	79.47% <0.00%> (-0.13%)	⬇️
... and 6 more

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[ttnghia]

I don't see any unit test for verifying the correctness of the function(s)? It would be nice to have a round trip test (row => col => row and col => row => col).

[hyperbolic2346]

I don't see any unit test for verifying the correctness of the function(s)? It would be nice to have a round trip test (row => col => row and col => row => col).

I agree, but the java directory isn't included in cudf tests. We have tests on the java side, but the strings aren't tested there yet. I have a test set that I use for testing, but I have to copy the row_conversion.cu down into cudf to run the tests. I was hoping that a solid testing framework would be a part of the spark-jni repo and this could move there, but it hasn't happened yet.

[hyperbolic2346]

rerun tests

[hyperbolic2346]

rerun tests

[hyperbolic2346]

@gpucibot merge