RFR: 8357996: Use "stdin.encoding" for reading System.in with InputStreamReader/Scanner [build/tools] [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-8357996 this PR is addressing is a sub-task of JDK-8356893 and is concerned with only areas related to build and tools.

Volkan Yazici has updated the pull request incrementally with one additional commit since the last revision:

  Provide fallback for `stdin.encoding` in `ExternalEditor`

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

Changes:
  - all: https://git.openjdk.org/jdk/pull/25541/files
  - new: https://git.openjdk.org/jdk/pull/25541/files/329180f5..c0dfa806

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=25541&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=25541&range=00-01

  Stats: 3 lines in 1 file changed: 2 ins; 0 del; 1 mod
  Patch: https://git.openjdk.org/jdk/pull/25541.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/25541/head:pull/25541

PR: https://git.openjdk.org/jdk/pull/25541