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

[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.

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Commit messages:
 - Initial commit
 - Merge branch 'master' of github.com:DamonGuy/jdk
 - Merge branch 'master' of github.com:DamonGuy/jdk
 - Initial commit for backout

Changes: https://git.openjdk.org/jdk/pull/23451/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=23451&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8344981
  Stats: 84 lines in 2 files changed: 83 ins; 0 del; 1 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