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

[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-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`

-------------

Changes:
  - all: https://git.openjdk.org/jdk/pull/25542/files
  - new: https://git.openjdk.org/jdk/pull/25542/files/d7751294..45bdc4fd

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=25542&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=25542&range=00-01

  Stats: 2 lines in 2 files changed: 0 ins; 0 del; 2 mod
  Patch: https://git.openjdk.org/jdk/pull/25542.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/25542/head:pull/25542

PR: https://git.openjdk.org/jdk/pull/25542