RFR: 6318027: BasicScrollBarUI does not disable timer when enclosing frame is disabled. [v4]

[Prasanta Sadhukhan]

> Issue is
> BasicScrollBarUI.ArrowButtonListener starts a timer in mousePressed(), and stops it in mouseReleased(). If the frame containing the scrollbar is disabled between the MOUSE_PRESSED and the MOUSE_RELEASED events, the mouseReleased() method is never called. If the frame is then re-enabled, the still-running timer causes it to scroll all the way to the end.
> Fix is to check if [ArrowButtonListener.handledEvent](https://github.com/openjdk/jdk/blame/ee839b7f0ebe471d3877cddd2c87019ccb8ee5ae/src/java.desktop/share/classes/javax/swing/plaf/basic/BasicScrollBarUI.java#L1567) is still set when ActionEvent is processed then stop the timer and reset this variable.
> 
> CI testing is green and also SwingSet2 JScrollPane scrolling with this modification..

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

  Stop the timer if frame is disabled

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

Changes:
  - all: https://git.openjdk.org/jdk/pull/20346/files
  - new: https://git.openjdk.org/jdk/pull/20346/files/00fd5e58..526c6a17

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=20346&range=03
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=20346&range=02-03

  Stats: 34 lines in 2 files changed: 19 ins; 0 del; 15 mod
  Patch: https://git.openjdk.org/jdk/pull/20346.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/20346/head:pull/20346

PR: https://git.openjdk.org/jdk/pull/20346