RFR: 8269280: (bf) Replace StringBuffer in *Buffer.toString()

[Aleksey Shipilev]

On Thu, 24 Jun 2021 08:31:58 GMT, Aleksey Shipilev <shade at openjdk.org> wrote:

> There is a StringBuffer use in X-Buffer template. The extra thread safety is not required there. In post-BiasedLocking times, this is gets worse, as every append is synchronized.
> 
> Additional testing:
>  - [x] `java/nio/Buffer` tests, verified current `toString` output is unchanged

Thanks for reviews!

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PR: https://git.openjdk.java.net/jdk/pull/4581