RFR: 8357994: Use "stdin.encoding" for reading System.in with InputStreamReader/Scanner [client]

[Volkan Yazici]

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-8357994 this PR is addressing is a sub-task of JDK-8356893 and is concerned with only areas related to client libraries.

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Commit messages:
 - Discard changes unrelated with client libraries
 - Revert superfluous changes
 - Revert changes to 3rd parties in `com/sun/org/apache`
 - Revert `PandocFilter` changes
 - Use `stdin.encoding` in `InputStreamReader` and `Scanner` instantiations

Changes: https://git.openjdk.org/jdk/pull/25543/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=25543&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8357994
  Stats: 17 lines in 3 files changed: 12 ins; 1 del; 4 mod
  Patch: https://git.openjdk.org/jdk/pull/25543.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/25543/head:pull/25543

PR: https://git.openjdk.org/jdk/pull/25543