RFR: 8374555: No need for visible input warning in s.s.u.Password when not reading from System.in

[Weijun Wang]

We should only print out `[WARNING: Input may be visible on screen]` when trying to read password from `System.in`. Don't print it if the password is read from a different URL.

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Commit messages:
 - the fix

Changes: https://git.openjdk.org/jdk/pull/29051/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=29051&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8374555
  Stats: 76 lines in 2 files changed: 74 ins; 0 del; 2 mod
  Patch: https://git.openjdk.org/jdk/pull/29051.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/29051/head:pull/29051

PR: https://git.openjdk.org/jdk/pull/29051