RFR: 8350703: Add standard system property stdin.encoding [v3]

[Naoto Sato]

On Wed, 23 Apr 2025 18:02:56 GMT, Stuart Marks <smarks at openjdk.org> wrote:

>> * Windows and Unix: set sprops.stdin_encoding if connected to a console
>> * Add specs for stdin.encoding
>> * Adjust specs to change "undefined" to "unspecified"
>> * Rewrite System.in spec to refer to new property and to clarify usage with classes that perform encoding
>> * Update property test
>
> Stuart Marks has updated the pull request incrementally with one additional commit since the last revision:
> 
>   Yet another minor bit of wordsmithing.

LGTM

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Marked as reviewed by naoto (Reviewer).

PR Review: https://git.openjdk.org/jdk/pull/24738#pullrequestreview-2791835320