[jdk17u-dev] RFR: 8280913: Create a regression test for JRootPane.setDefaultButton() method

[Goetz Lindenmaier]

I backport this for parity with 17.0.5-oracle.

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Commit messages:
 - Backport 51b53a821bb3cfb962f80a637f5fb8cde988975a

Changes: https://git.openjdk.org/jdk17u-dev/pull/608/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk17u-dev&pr=608&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8280913
  Stats: 111 lines in 1 file changed: 111 ins; 0 del; 0 mod
  Patch: https://git.openjdk.org/jdk17u-dev/pull/608.diff
  Fetch: git fetch https://git.openjdk.org/jdk17u-dev pull/608/head:pull/608

PR: https://git.openjdk.org/jdk17u-dev/pull/608