C++: Add cast from Dictionary to plain arrays

[asfimport]

Cast dictionary arrays to the plain representation.

Reporter: Uwe Korn / @xhochy
Assignee: Uwe Korn / @xhochy

Related issues:

• [C++] Type casting function kernel suite (is part of)

_{Note: This issue was originally created as ARROW-1513. Please see the migration documentation for further details.}

[asfimport]

Wes McKinney / @wesm:
This might be most easily implemented by using Take, i.e. Take(ctx, dictionary, indices, &out), which we ought to implement soon.

[asfimport]

Uwe Korn / @xhochy:
We can implement this soon using Take but I'm taking a shot at this currently to get the functionality in parquet-cpp and to understand the new compute library.

[asfimport]

Wes McKinney / @wesm:
Issue resolved by pull request 1086
#1086