[Rust] impl AsRef for StringBuilder/BinaryBuilder

[asfimport]

The current implementation of Arrow forces the users to pass a reference to the append_value methods of StringBuilder/BinaryBuilder. Whereas it is passed by value for other types of builders.  This patch suggests adding impl AsRef<[u8]> rather than the current &[u8] parameter.

Some background for this issue: I have a Rust derive macro which converts the specified struct to Arrow data. This macro assumes everything is passed by value to Arrow, hence the dilemma. 

Reporter: Max Meldrum

Externally tracked issue: #9570

PRs and other links:

• GitHub Pull Request #9570

_{Note: This issue was originally created as ARROW-11777. Please see the migration documentation for further details.}

[asfimport]

Andrew Lamb / @alamb:
Issue resolved by pull request 9570
#9570