RFR: 8361972: Clarify the condition of System.console() about standard input/output [v3]

[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 with a new target base due to a merge or a rebase. The incremental webrev excludes the unrelated changes brought in by the merge/rebase. The pull request contains four additional commits since the last revision:

 - Wording change, isTerminal() always returns true
 - Merge branch 'master' into JDK-8361972-System-console-condition
 - Wording modification
 - initial commit

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Changes:
  - all: https://git.openjdk.org/jdk/pull/26299/files
  - new: https://git.openjdk.org/jdk/pull/26299/files/e2a64c95..a3b39049

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=26299&range=02
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=26299&range=01-02

  Stats: 20447 lines in 622 files changed: 13483 ins; 4316 del; 2648 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