[jdk21u-dev] RFR: 8326606: Test javax/swing/text/BoxView/6494356/bug6494356.java performs a synchronization on a value based class

[Goetz Lindenmaier]

I backport this for parity with 21.0.9-oracle

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Commit messages:
 - Backport 013aff87ce7ece5cd4676aa452557ea3f222cede

Changes: https://git.openjdk.org/jdk21u-dev/pull/1939/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk21u-dev&pr=1939&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8326606
  Stats: 135 lines in 1 file changed: 135 ins; 0 del; 0 mod
  Patch: https://git.openjdk.org/jdk21u-dev/pull/1939.diff
  Fetch: git fetch https://git.openjdk.org/jdk21u-dev.git pull/1939/head:pull/1939

PR: https://git.openjdk.org/jdk21u-dev/pull/1939