[C++] Provide ArrayBuilder::AppendScalar

[asfimport]

It would be useful to be able to append a Scalar (and/or ScalarVector) to an ArrayBuilder. For example, in #9621 (comment) (ARROW-11591) this could be used to accumulate an array of expected grouped aggregation results using existing scalar aggregate kernels

Reporter: Ben Kietzman / @bkietz
Assignee: David Li / @lidavidm

Related issues:

• [C++] Optimize ArrayBuilder::AppendScalar (is related to)

PRs and other links:

• GitHub Pull Request #10579

_{Note: This issue was originally created as ARROW-11932. Please see the migration documentation for further details.}

[asfimport]

David Li / @lidavidm:
Was resolved as part of #10511.