RFR: 8357993: Use "stdin.encoding" for reading System.in with InputStreamReader/Scanner [hotspot] [v2]

[Serguei Spitsyn]

On Mon, 2 Jun 2025 18:39:33 GMT, Volkan Yazici <vyazici at openjdk.org> wrote:

>> Passes the `Charset` read from the `stdin.encoding` system property while creating `InputStreamReader` or `Scanner` instances for `System.in`.
>> 
>> `stdin.encoding` is a recently added property for Java 25 in [JDK-8350703](https://bugs.openjdk.org/browse/JDK-8350703). Employing it throughout the entire code base is addressed by the parent ticket [JDK-8356893](https://bugs.openjdk.org/browse/JDK-8356893). JDK-8357993 this PR is addressing is a sub-task of JDK-8356893 and is concerned with only areas related to Hotspot.
>
> Volkan Yazici has updated the pull request incrementally with one additional commit since the last revision:
> 
>   Provide fallback for `stdin.encoding`

Looks okay to me.

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Marked as reviewed by sspitsyn (Reviewer).

PR Review: https://git.openjdk.org/jdk/pull/25542#pullrequestreview-2901163257