Expose stream parameter in public nvtext ngram APIs

[davidwendt]

Description

Add stream parameter to public APIs:

• nvtext::generate_ngrams()
• nvtext::generate_character_ngrams()
• nvtext::hash_character_ngrams()
• nvtext::ngrams_tokenize()

Also cleaned up some of the doxygen comments.
And also fixed a spelling mistake in the jaccard.cu source that was bothering me.

Reference #13744

Checklist

• I am familiar with the Contributing Guidelines.
• New or existing tests cover these changes.
• The documentation is up to date with these changes.

[vyasr]

Looks good, but same request for tests as on #14060

[davidwendt]

@vyasr How do I run these tests locally?

[vyasr]

@vyasr How do I run these tests locally?

The easiest way to run the test with the appropriate configuration is to use ctest. ctest -R STREAM_TEXT_TEST will work for this one. If you execute the test executable directly it will run, but without the appropriate stream configuration; to do that correctly, you also need to set the appropriate environment variables:

GTEST_CUDF_STREAM_MODE=new_testing_default LD_PRELOAD=/path/to/build/cudf_identify_stream_usage_mode_testing /path/to/test/executable

[vyasr]

LGTM. I'm changing the labels to mark this PR as breaking now though since the separator is no longer optional.

[davidwendt]

/merge