RFR: 8295006: Colored text is not shown on disabled checkbox and radiobutton with GTK LAF for bug4314194

[Abhishek Kumar]

Existing test `open/test/jdk/javax/swing/JRadioButton/4314194/bug4314194.java` was not showing colored text for disabled checkbox and radiobutton in GTK LAF.

The fix is to get the disabled state color for checkbox and radiobutton from UIManager if it exists. 

Test case `open/test/jdk/javax/swing/JRadioButton/4314194/bug4314194.java` has been checked in CI pipeline. Link is attached in JBS.

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

Commit messages:
 - 8295006 entry removed from problem lists
 - Fix for disabled checkbox and radiobutton colored text

Changes: https://git.openjdk.org/jdk/pull/10755/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=10755&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8295006
  Stats: 13 lines in 2 files changed: 12 ins; 1 del; 0 mod
  Patch: https://git.openjdk.org/jdk/pull/10755.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/10755/head:pull/10755

PR: https://git.openjdk.org/jdk/pull/10755