[jdk21u-dev] RFR: 8327137: Add test for ConcurrentModificationException in BasicDirectoryModel

[Andrew Lu]

I backport this for parity with 21.0.3-oracle.

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Commit messages:
 - Backport 9731b1c8b02d957985f4fb40acd93fb67747a9f0

Changes: https://git.openjdk.org/jdk21u-dev/pull/584/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk21u-dev&pr=584&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8327137
  Stats: 273 lines in 1 file changed: 273 ins; 0 del; 0 mod
  Patch: https://git.openjdk.org/jdk21u-dev/pull/584.diff
  Fetch: git fetch https://git.openjdk.org/jdk21u-dev.git pull/584/head:pull/584

PR: https://git.openjdk.org/jdk21u-dev/pull/584