RFR: 8361972: Clarify the condition of System.console() about standard input/output [v4]

[Naoto Sato]

> This accompanies the fix for [JDK-8361613](https://bugs.openjdk.org/browse/JDK-8361613), which restricts `System.console()` to return a `Console` instance only when both standard input and output are connected to a terminal. The change here is solely a specification clarification and tightening of the `java.io.Console` javadoc to reflect this behavior. We are separating the spec clarification because the fix itself may be backported to prior LTS releases without requiring a Maintenance Review process.

Naoto Sato has updated the pull request incrementally with one additional commit since the last revision:

  Reflecting review comments

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Changes:
  - all: https://git.openjdk.org/jdk/pull/26299/files
  - new: https://git.openjdk.org/jdk/pull/26299/files/a3b39049..8453c434

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=26299&range=03
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=26299&range=02-03

  Stats: 11 lines in 1 file changed: 0 ins; 2 del; 9 mod
  Patch: https://git.openjdk.org/jdk/pull/26299.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/26299/head:pull/26299

PR: https://git.openjdk.org/jdk/pull/26299