RFR: JDK-8302323 Add repeat methods to StringBuilder/StringBuffer [v8]

[Sergey Tsypanov]

On Fri, 3 Mar 2023 19:04:22 GMT, Jim Laskey <jlaskey at openjdk.org> wrote:

>> Add the ability to repeatedly append char and CharSequence data to StringBuilder/StringBuffer.
>
> Jim Laskey has updated the pull request incrementally with one additional commit since the last revision:
> 
>   Expand test for StringBuffer and illegal code points

Should we also have overloaded method accepting position to insert repeated value? Smth like `repeat(int pos, char c, int count)`?

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PR: https://git.openjdk.org/jdk/pull/12728