RFR: 8354219 : Automate javax/swing/JComboBox/ComboPopupBug.java [v7]

[Anass Baya]

> This test was designed to manually verify that clicking on the JComboBox when the frame containing it is about to close does not cause an IllegalStateException.
> 
> The test allowed the tester extra time to click on the JComboBox when closing the frame by adding a Thread.sleep() in the close button handler.
> 
> In this test, a JComboBox is displayed with a Close button at the bottom. The tester should click the Close button, then try to click the JComboBox arrow button to display the popup.
> 
> In the automated test, we save the JComboBox  location size before closing the frame. We then use this information to click on the JComboBox right before the frame is closed.

Anass Baya has updated the pull request incrementally with three additional commits since the last revision:

 - Put the frame in the centre of the screen.
   
   Co-authored-by: Alexey Ivanov <alexey.ivanov at oracle.com>
 - library regtesthelpers is no more used
 - Alexey's proposed enhancement

-------------

Changes:
  - all: https://git.openjdk.org/jdk/pull/24624/files
  - new: https://git.openjdk.org/jdk/pull/24624/files/35ad53ca..0098a81c

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=24624&range=06
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=24624&range=05-06

  Stats: 53 lines in 1 file changed: 24 ins; 20 del; 9 mod
  Patch: https://git.openjdk.org/jdk/pull/24624.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/24624/head:pull/24624

PR: https://git.openjdk.org/jdk/pull/24624