[R] Add functions to write RecordBatch or Schema to Message value, then read back

[asfimport]

Follow up work to ARROW-3499

Reporter: Wes McKinney / @wesm
Assignee: Romain Francois / @romainfrancois

PRs and other links:

• GitHub Pull Request #4673

_{Note: This issue was originally created as ARROW-3732. Please see the migration documentation for further details.}

[asfimport]

Wes McKinney / @wesm:
@romainfrancois seems like you may have this already, or close to it?