<Swing Dev> RFR: 8266249: javax/swing/JPopupMenu/7156657/bug7156657.java fails on macOS

[Alexander Zuev]

Fixed popup position taking into account its offset
Added a lot of screenshots taking to better understand failures should they happen down the line

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Commit messages:
 - 8266249: javax/swing/JPopupMenu/7156657/bug7156657.java fails on macOS

Changes: https://git.openjdk.java.net/jdk/pull/3844/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=3844&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8266249
  Stats: 41 lines in 1 file changed: 40 ins; 0 del; 1 mod
  Patch: https://git.openjdk.java.net/jdk/pull/3844.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/3844/head:pull/3844

PR: https://git.openjdk.java.net/jdk/pull/3844