RFR: 7175397: The divider color is not changed to green when dragging for Nimbus LaF. [v3]

[Prasanta Sadhukhan]

> SplitPaneDivider.draggingColor UIProperty was not honoured in Nimbus L&F. 
> Added support for setting SplitPane dragging color for Nimbus L&F by drawing a fillRect of the set color as done in BasicLookAndFeel.
> The fix relies on `continuousLayout` property being false by default which is enabled for Nimbus, which is set to default false now, same as in other L&F. I think it was set true just to have documented default value in JDK-6937415
> 
> closed test mentioned in JBS is used for fix check.
> All jtreg swing tests are ok along with SwingSet2 JSplitPane demo in Nimbus L&F.

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

  Review comment fix. Add test

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

Changes:
  - all: https://git.openjdk.org/jdk/pull/9937/files
  - new: https://git.openjdk.org/jdk/pull/9937/files/1dafa3d6..ee0fd693

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=9937&range=02
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=9937&range=01-02

  Stats: 130 lines in 2 files changed: 110 ins; 19 del; 1 mod
  Patch: https://git.openjdk.org/jdk/pull/9937.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/9937/head:pull/9937

PR: https://git.openjdk.org/jdk/pull/9937