RFR: 8331708: jdk/internal/jline/RedirectedStdOut.java times-out on macosx-aarch64

[Jan Lahoda]

When integrating:
https://github.com/openjdk/jdk/pull/18996

I've forgot to push one last commit which was stabilizing the test of Mac OS/X. I am sorry for that.

The test will create a pseudo terminal, and change the current process stdin/stdout to write into the pty. But, there's nothing reading from the pty on the other side. This mostly works, OK, but the `ProcessTools` will write a debug log into `System.out` (which will write to stdout, which is the pty), and that blocks on Mac OS/X, presumably because there's nothing reading from the pty.

This patch changes the `System.out` for the main process to a scratch value, so no write to stdout/FD 1 is done, and no blocking should happen. (The process' stdout/FD 1 should remain attached to the pty.)

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Commit messages:
 - 8331708: jdk/internal/jline/RedirectedStdOut.java times-out on macosx-aarch64

Changes: https://git.openjdk.org/jdk/pull/19097/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=19097&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8331708
  Stats: 8 lines in 1 file changed: 6 ins; 1 del; 1 mod
  Patch: https://git.openjdk.org/jdk/pull/19097.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/19097/head:pull/19097

PR: https://git.openjdk.org/jdk/pull/19097