RFR: JDK-6690019: JOptionPane obscured behind an always on top JFrame hangs UI [v3]

[Prasanta Sadhukhan]

> A JOptionPane message dialog owned by a JFrame which is not always on top can be obscured behind an `"always on top" JFrame`. Since the option pane is modal, one can't move the "always on top frame" to reveal it, so the application effectively hangs as we cannot dismiss the option pane dialog
> Fix is to make sure the option pane dialog is always on top....

Prasanta Sadhukhan has updated the pull request incrementally with one additional commit since the last revision:

  Add test

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Changes:
  - all: https://git.openjdk.org/jdk/pull/16060/files
  - new: https://git.openjdk.org/jdk/pull/16060/files/531207fa..419c21b9

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=16060&range=02
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=16060&range=01-02

  Stats: 4 lines in 1 file changed: 0 ins; 0 del; 4 mod
  Patch: https://git.openjdk.org/jdk/pull/16060.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/16060/head:pull/16060

PR: https://git.openjdk.org/jdk/pull/16060