[jdk8u-dev] RFR: 8129940: JRadioButton does not honor non-standard FocusTraversalKeys

[Zhengyu Gu]

I would like to backport this patch to openjdk8u for parity with Oracle 
8u311.

The original bug: https://bugs.openjdk.java.net/browse/JDK-8129940
The original patch: 
[http://hg.openjdk.java.net/jdk9/jdk9/jdk/rev/fbf897c33625](https://hg.openjdk.java.net/jdk9/jdk9/jdk/rev/fbf897c33625)

The jdk9 patch does not apply cleanly, but only conflict is copyright 
year of `BasicRadioButtonUI.java` file.

Test:
- [x] Included `FocusTraversal/FocusTraversal.java` test fails without patch and passes with it on Linux x86_64

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Commit messages:
 - 8129940: JRadioButton does not honor non-standard FocusTraversalKeys

Changes: https://git.openjdk.java.net/jdk8u-dev/pull/41/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk8u-dev&pr=41&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8129940
  Stats: 166 lines in 2 files changed: 154 ins; 0 del; 12 mod
  Patch: https://git.openjdk.java.net/jdk8u-dev/pull/41.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk8u-dev pull/41/head:pull/41

PR: https://git.openjdk.java.net/jdk8u-dev/pull/41