[C++] Allow reordering fields of a StructArray via casting

[asfimport]

Follow-up to ARROW-15643 and possibly required for full handling of nested field refs in scanning. We may need to add a cast option to allow this since this can cause ambiguities.

Reporter: David Li / @lidavidm

Related issues:

• [C++] Kernel to select subset of fields of a StructArray (relates to)

_{Note: This issue was originally created as ARROW-16112. Please see the migration documentation for further details.}