Enable casting to int64, uint64, and double in AST code.

[vyasr]

This PR resolves #8979, adding support for a few casting operators in AST code. These operators can be used to perform operations between columns with mismatched data types without materializing intermediates as new columns.

[codecov]

Codecov Report

Merging #9379 (b704f3a) into branch-21.12 (ab4bfaa) will increase coverage by 0.04%.
The diff coverage is 0.00%.

@@               Coverage Diff                @@
##           branch-21.12    #9379      +/-   ##
================================================
+ Coverage         10.79%   10.83%   +0.04%     
================================================
  Files               116      117       +1     
  Lines             18869    19442     +573     
================================================
+ Hits               2036     2106      +70     
- Misses            16833    17336     +503     

Impacted Files	Coverage Δ
python/cudf/cudf/__init__.py	0.00% <0.00%> (ø)
python/cudf/cudf/_lib/__init__.py	0.00% <ø> (ø)
python/cudf/cudf/core/_base_index.py	0.00% <0.00%> (ø)
python/cudf/cudf/core/column/categorical.py	0.00% <0.00%> (ø)
python/cudf/cudf/core/column/column.py	0.00% <0.00%> (ø)
python/cudf/cudf/core/column/datetime.py	0.00% <0.00%> (ø)
python/cudf/cudf/core/column/lists.py	0.00% <0.00%> (ø)
python/cudf/cudf/core/column/numerical.py	0.00% <0.00%> (ø)
python/cudf/cudf/core/column/string.py	0.00% <0.00%> (ø)
python/cudf/cudf/core/column/struct.py	0.00% <0.00%> (ø)
... and 76 more

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[karthikeyann]

SFINAE and type traits.

[bdice]

Also add these operators to UnaryOperator.java:
https://github.com/rapidsai/cudf/blob/branch-21.12/java/src/main/java/ai/rapids/cudf/ast/UnaryOperator.java

Otherwise, looks good to me!

[codereport]

lgtm 👍

[karthikeyann]

LGTM 👍

[jlowe]

Since the Java code was updated as part of this PR to add bindings to these new AST operators, it would be nice to have Java tests to verify those bindings are operating correctly. Happy to do this as a followup if needed.

[vyasr]

@jlowe if you don't mind adding the tests separately that would be great. It would be good to get this merged so I can work on some next steps in the AST code. If you don't get around to writing the tests let me know, I can always make the follow-up myself.

[vyasr]

@gpucibot merge