RFR: 8316104: Open source several Swing SplitPane and RadioButton related tests

[Tejesh R]

Open sourcing these Swing SplitPane and RadioButton related tests:

javax/swing/JSplitPane/4147653/bug4147653.java
javax/swing/JSplitPane/4870674/bug4870674.java
javax/swing/JRadioButton/4823809/bug4823809.java

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Commit messages:
 - Open sourcing few SplitPane and RadioButton test

Changes: https://git.openjdk.org/jdk/pull/15738/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=15738&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8316104
  Stats: 332 lines in 3 files changed: 332 ins; 0 del; 0 mod
  Patch: https://git.openjdk.org/jdk/pull/15738.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/15738/head:pull/15738

PR: https://git.openjdk.org/jdk/pull/15738