[Rust] Add an `into_inner()` method to ipc::writer::StreamWriter

[asfimport]

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.

Reporter: Eric Burden / @ericwburden
Assignee: Eric Burden / @ericwburden

PRs and other links:

• GitHub Pull Request #9858

_{Note: This issue was originally created as ARROW-12160. Please see the migration documentation for further details.}

[asfimport]

Andrew Lamb / @alamb:
Issue resolved by pull request 9858
#9858