Add sequence_type parameter to cudf::strings::title function

[davidwendt]

Closes #8596 #8597

Adds a sequence_type parameter to help control how words are delimited within a string when processing the title() logic.

std::unique_ptr<column> title(
  strings_column_view const& input,
  string_character_types sequence_type = string_character_types::ALPHA,
  rmm::mr::device_memory_resource* mr  = rmm::mr::get_current_device_resource());

The default ALPHA type preserves the original behavior which matches with the Pandas str.title() where the first character after a non-ALPHA is upper-cased and the rest are lower-cased. Likewise, specifying ALPHANUM will treat a sequence of alphanumeric characters as a word and upper-case only after a non-ALPHANUM (e.g. whitespace).

The sequence_type type is declared in the char_types.hpp header and so these types can be reused in this API.

The following usage should satisfy the #8597 feature request.

   cudf::strings_column_view view(input); // input strings column
   auto result = cudf::strings::title(view, cudf::string_character_types::ALPHANUM);

The ALPHANUM set contains all alphanumeric character types which leaves out only SPACE which is the set of whitespace characters.

The gtests for cudf::strings::title() have been updated to include test-cases using ALPHANUM.

[codecov]

Codecov Report

Merging #8602 (fa32c39) into branch-21.08 (58438c0) will increase coverage by 0.36%.
The diff coverage is n/a.

❗ Current head fa32c39 differs from pull request most recent head 95a82fc. Consider uploading reports for the commit 95a82fc to get more accurate results

@@               Coverage Diff                @@
##           branch-21.08    #8602      +/-   ##
================================================
+ Coverage         82.63%   83.00%   +0.36%     
================================================
  Files               109      109              
  Lines             17869    18222     +353     
================================================
+ Hits              14766    15125     +359     
+ Misses             3103     3097       -6     

Impacted Files	Coverage Δ
python/cudf/cudf/core/abc.py	86.36% <0.00%> (-1.45%)	⬇️
python/cudf/cudf/io/feather.py	100.00% <0.00%> (ø)
python/cudf/cudf/comm/serialize.py	0.00% <0.00%> (ø)
python/cudf/cudf/_fuzz_testing/io.py	0.00% <0.00%> (ø)
python/cudf/cudf/utils/applyutils.py	100.00% <0.00%> (ø)
python/dask_cudf/dask_cudf/_version.py	0.00% <0.00%> (ø)
python/cudf/cudf/_fuzz_testing/fuzzer.py	0.00% <0.00%> (ø)
python/cudf/cudf/utils/hash_vocab_utils.py	100.00% <0.00%> (ø)
python/dask_cudf/dask_cudf/io/tests/test_csv.py	100.00% <0.00%> (ø)
python/dask_cudf/dask_cudf/io/tests/test_orc.py	100.00% <0.00%> (ø)
... and 44 more

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[rgsl888prabhu]

A small suggestion, rest looks good.

[davidwendt]

@gpucibot merge