RFR: 8226990: GTK & Nimbus LAF: Tabbed pane's background color is not expected one when change the opaque checkbox. [v6]

[Abhishek Kumar]

> JTabbedPane's content area, tab area and tab background color are not as expected when opaque is set to true or false. 
> The proposed fix is to handle the TabbedPane's background color in installed LAFs. Manual test is added to support the fix and there is no regression caused by the fix. 
> 
> Proposed fix is tested in Ubuntu 22.04 and Oracle linux.
> 
> CI link is posted in JBS.

Abhishek Kumar has updated the pull request incrementally with one additional commit since the last revision:

  Test update

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

Changes:
  - all: https://git.openjdk.org/jdk/pull/17720/files
  - new: https://git.openjdk.org/jdk/pull/17720/files/563be986..4a878022

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=17720&range=05
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=17720&range=04-05

  Stats: 11 lines in 1 file changed: 1 ins; 1 del; 9 mod
  Patch: https://git.openjdk.org/jdk/pull/17720.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/17720/head:pull/17720

PR: https://git.openjdk.org/jdk/pull/17720