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ARROW-12160: [Rust] Add `into_inner()` to StreamWriter

Add an `into_inner()` method to `ipc::writer::StreamWriter`, allowing users to recover the underlying writer, consuming the StreamWriter. Essentially exposes `into_inner()` from the BufWriter contained in the StreamWriter. The StreamWriter will 'finish' itself if not already finished when returning the writer.

Also added `ArrowError::From<std::io::IntoInnerError>` conversion to allow for ergonomic return of the potential `IntoInnerError` returned by `BufWriter.into_inner()`.

Closes #9858 from ericwburden/into-inner-fn-for-stream-writer

Authored-by: Eric Burden <eric.w.burden@gmail.com>
Signed-off-by: Andrew Lamb <andrew@nerdnetworks.org>