[C++] Add option to is_nan kernel to return true on null

[asfimport]

Currently the is_nan C++ kernel returns null on null values. Consider adding a boolean option to this kernel to control whether to consider null as NaN. This would allow the code added in ARROW-12850 to be much simplified.

Reporter: Ian Cook / @ianmcook

Related issues:

• [C++][R] Option for is_nan(null) to evaluate to false or true (duplicates)
• [R] is.nan() evaluates to null on Arrow null values (relates to)
• [C++] Add option to is_null kernel to return true on NaN (is related to)

_{Note: This issue was originally created as ARROW-13366. Please see the migration documentation for further details.}

[github-actions]

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