[jdk11u-dev] RFR: 8286620: Create regression test for verifying setMargin() of JRadioButton

[Goetz Lindenmaier]

I backport this for parity with 11.0.21-oracle.

I had to replace the """ string.

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Commit messages:
 - Backport 67f1bd7ff1bb218fd6de9ef1e957f729013e133c

Changes: https://git.openjdk.org/jdk11u-dev/pull/2015/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk11u-dev&pr=2015&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8286620
  Stats: 135 lines in 1 file changed: 135 ins; 0 del; 0 mod
  Patch: https://git.openjdk.org/jdk11u-dev/pull/2015.diff
  Fetch: git fetch https://git.openjdk.org/jdk11u-dev.git pull/2015/head:pull/2015

PR: https://git.openjdk.org/jdk11u-dev/pull/2015