[C++] Refactor filter/take kernels to use Datum instead of overloads

[asfimport]

Followup to ARROW-6784. See discussion on https://github.com/apache/arrow/pull/5686, as well as ARROW-6959.

Reporter: Neal Richardson / @nealrichardson
Assignee: Wes McKinney / @wesm

Related issues:

• [C++] C++ array kernels framework and execution buildout (umbrella issue) (is a child of)
• [C++][Compute] Formalize "metafunction" concept (relates to)

_{Note: This issue was originally created as ARROW-7009. Please see the migration documentation for further details.}

[asfimport]

Joris Van den Bossche / @jorisvandenbossche:
At least for filter it seems this has already been done

[asfimport]

Wes McKinney / @wesm:
This was done in 199d089