RFR: 8344981: [REDO] JDK-6672644 JComboBox still scrolling if switch to another window and return back [v5]

[Damon Nguyen]

> Redo for JComboBox infinite scrolling issue. The issue is that when a scrollbar is clicked and held, if the user switches focus (ex: ALT+TAB) while scrolling, when focused is returned to the scrolling application, the JComboBox will still be scrolling even though nothing it being clicked.
> 
> Previously, a KeyboardFocusListener was added to determine the focus. However, there was a memory leak on Windows and Ubuntu. This current implementation uses the current FocusManager and is overall a cleaner, simpler approach.
> 
> CI testing is green on all platforms.

Damon Nguyen has updated the pull request incrementally with one additional commit since the last revision:

  Add helper method

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

Changes:
  - all: https://git.openjdk.org/jdk/pull/23451/files
  - new: https://git.openjdk.org/jdk/pull/23451/files/3a7bf130..ce106acd

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=23451&range=04
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=23451&range=03-04

  Stats: 12 lines in 1 file changed: 6 ins; 4 del; 2 mod
  Patch: https://git.openjdk.org/jdk/pull/23451.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/23451/head:pull/23451

PR: https://git.openjdk.org/jdk/pull/23451