RFR: 8342508: Use latch in BasicMenuUI/bug4983388.java instead of delay

[Alexey Ivanov]

Use a `CountDownLatch` in `javax/swing/plaf/basic/BasicMenuUI/4983388/bug4983388.java` instead of delay.

The latch provides a direct way to synchronise EDT and main thread, the test will finish quicker.

I ran the updated test a few times with `JTREG=REPEAT_COUNT=20`, the test always passed in the CI.

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Commit messages:
 - 8342508: Use latch in BasicMenuUI/bug4983388.java instead of delay

Changes: https://git.openjdk.org/jdk/pull/21585/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=21585&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8342508
  Stats: 42 lines in 1 file changed: 23 ins; 10 del; 9 mod
  Patch: https://git.openjdk.org/jdk/pull/21585.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/21585/head:pull/21585

PR: https://git.openjdk.org/jdk/pull/21585