RFR: 8358809: better link to stdin.encoding from java.lang.IO

[Stuart Marks]

Use a link of the form `System##stdin.encoding` to link directly to the system property's description.

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Commit messages:
 - 8358809: better link to stdin.encoding from java.lang.IO

Changes: https://git.openjdk.org/jdk/pull/25676/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=25676&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8358809
  Stats: 1 line in 1 file changed: 0 ins; 0 del; 1 mod
  Patch: https://git.openjdk.org/jdk/pull/25676.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/25676/head:pull/25676

PR: https://git.openjdk.org/jdk/pull/25676