RFR: 8374555: No need for visible input warning in s.s.u.Password when not reading from System.in [v2]

[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.

Weijun Wang has updated the pull request incrementally with one additional commit since the last revision:

  warn only if VM is booted; more comments

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Changes:
  - all: https://git.openjdk.org/jdk/pull/29051/files
  - new: https://git.openjdk.org/jdk/pull/29051/files/2bafe786..29612746

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=29051&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=29051&range=00-01

  Stats: 5 lines in 1 file changed: 4 ins; 0 del; 1 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