[C++] Expose type casts as generic callable object that can write into pre-allocated memory

[asfimport]

Follow up to ARROW-229. Some projects may reuse temporary buffers, so presuming you know how much memory to allocate, you will want to be able to invoke the cast closures in generic way.

The API created in doing this should be deemed experimental as we iterate towards a more generic analytical kernel evaluation model

Reporter: Wes McKinney / @wesm
Assignee: Wes McKinney / @wesm

Related issues:

• [C++] Type casting function kernel suite (Is contained by)
• [C++] Implement safe casts for primitive types (relates to)

_{Note: This issue was originally created as ARROW-1481. Please see the migration documentation for further details.}

[asfimport]

Wes McKinney / @wesm:
Started working on this

[asfimport]

Wes McKinney / @wesm:
Part of patch for ARROW-1156: #1063

[asfimport]

Wes McKinney / @wesm:
Resolved in de2edc8