[C++] Restore function that can read a complete encapsulated record batch message

[asfimport]

In recent refactoring around the stream and file format implementations, the ipc::RecordBatchReader class was removed, here it is in Arrow 0.1

https://github.com/apache/arrow/blob/apache-arrow-0.1.0/cpp/src/arrow/ipc/adapter.h#L81

see implementation at

https://github.com/apache/arrow/blob/apache-arrow-0.1.0/cpp/src/arrow/ipc/adapter.cc#L389

For shared memory IPC, it would be useful to restore this functionality, possibly as a single function rather than a class. We should also make sure this is properly documented in https://github.com/apache/arrow/blob/master/format/IPC.md

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

_{Note: This issue was originally created as ARROW-660. Please see the migration documentation for further details.}

[asfimport]

Wes McKinney / @wesm:
This was done in the patch for ARROW-621: https://github.com/apache/arrow/blob/master/cpp/src/arrow/ipc/reader.h#L122