[REVIEW] Port NVStrings datetime conversion ops to cudf strings column

[davidwendt]

This is porting of the NVStrings datetime conversion methods to strings_column_view functions.

NVStrings methods addressed in this PR:

timestamp2long
long2timestamp

New names will be: to_timestamps, from_timestamps() respectively

[codecov]

Codecov Report

Merging #3232 into branch-0.11 will not change coverage.
The diff coverage is n/a.

@@             Coverage Diff             @@
##           branch-0.11   #3232   +/-   ##
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  Coverage         87.3%   87.3%           
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  Files               49      49           
  Lines             9214    9214           
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  Hits              8044    8044           
  Misses            1170    1170

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[harrism]

One suggestion.

[jrhemstad]

@trxcllnt does simt::chrono have https://en.cppreference.com/w/cpp/chrono/parse and https://en.cppreference.com/w/cpp/chrono/format?

If so, this PR could be vastly, vastly simplified by using those.

All review comments addressed.

[harrism]

@davidwendt This is ready to merge once you resolve conflicts.

[rwlee]

As part of this port, can we get fixes for some of the issues opened up against these operators?

-- Negative timestamp support for from_timestamp (long2timestamp), #3116
-- The 2 issues in this github issue #3353, data corrupt from reading past end of string and blind consumption of literals. The data corruption from reading past the end of string may be fixed because the length is no longer unsigned.
-- Documentation update to accurately reflect functionality, resolves #3118
-- Ideally something that fits this feature request too #3320

[davidwendt]

As part of this port, can we get fixes for some of the issues opened up against these operators?

-- Negative timestamp support for from_timestamp (long2timestamp), #3116
-- The 2 issues in this github issue #3353, data corrupt from reading past end of string and blind consumption of literals. The data corruption from reading past the end of string may be fixed because the length is no longer unsigned.
-- Documentation update to accurately reflect functionality, resolves #3118
-- Ideally something that fits this feature request too #3320

All of these will require significant work. This PR is intended to just port the existing function. New follow on PRs will be created to address these issues.

[harrism]

Crap, accidentally deleted a " in the CMakeLists.txt when I resolved conflicts. Sorry @davidwendt .

All comments addressed.