Add delimiter parameter to cudf::strings::capitalize()

[davidwendt]

Closes #8597

Add a parameter to the cudf::strings::capitalize() function to support capitalizing characters after a specified delimiter. This should meet the requirements of #8597 by passing a single ' ' character string as follows:

    auto results = cudf::strings::capitalize(strings_view, std::string(" "));

The new parameter has a default of empty string that keeps the current behavior so no updates are required to python/cython layer. The new parameter requires this PR to be a breaking change.

The source code for title() and capitalize() were further refactored using the CRTP pattern since much of the main internal code logic is the same.

This PR also includes additional gtests for this new parameter as well as adding some missing tests for empty columns.

[davidwendt]

@jlowe Can you verify this API is sufficient for #8597 ?

[jlowe]

Can you verify this API is sufficient for #8597 ?

Yes, this should be sufficient to match the behavior of Spark's initcap function. At first I was worried that Spark's toTitleCase() method, which is used by initcap, changes characters to uppercase and never lowercase any characters in the string. However the initcap implementation lowercases the string before calling toTitleCase(), so we should be good as far as matching the initcap behavior.

[codecov]

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[davidwendt]

rerun tests

[davidwendt]

rerun tests

[davidwendt]

@gpucibot merge