RFR: 8343123: Nimbus: javax/swing/JInternalFrame/bug6726866.java does not have green undecorated window [v3]

[Prasanta Sadhukhan]

> Test fails in NimbusL&F as DesktopPane does not have green background as set by the user, which is because, the auto-generated [DesktopPanePainter class](https://github.com/openjdk/jdk/blob/eb40a88f4076360708402454a494907e8c0c845d/src/java.desktop/share/classes/javax/swing/plaf/nimbus/SynthPainterImpl.java#L100-L102) which has pre-coded color values does not honour user-defined color.
> 
> Fix is to make sure user-defined DesktopPane background color is honoured and is painted and only auto-generated class for L&F derived colors.
> CI is ok..

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

  wildcard

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

Changes:
  - all: https://git.openjdk.org/jdk/pull/22057/files
  - new: https://git.openjdk.org/jdk/pull/22057/files/df974a04..df5d0f30

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=22057&range=02
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=22057&range=01-02

  Stats: 11 lines in 1 file changed: 8 ins; 0 del; 3 mod
  Patch: https://git.openjdk.org/jdk/pull/22057.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/22057/head:pull/22057

PR: https://git.openjdk.org/jdk/pull/22057