RFR: 8299713: Test javax/swing/JTableHeader/6889007/bug6889007.java failed: Wrong type of cursor

[Prasanta Sadhukhan]

Issue seems to be very old, very intermittent bug which is not reproducible in repeated test run,
so added some stability fixes like accessing swing components in EDT, delay, frame dispose and take a screenshot during fail.
Multiple runs on CI platforms is ok.

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Commit messages:
 - 8299713: Test javax/swing/JTableHeader/6889007/bug6889007.java failed: Wrong type of cursor
 - 8299713: Test javax/swing/JTableHeader/6889007/bug6889007.java failed: Wrong type of cursor

Changes: https://git.openjdk.org/jdk/pull/12181/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=12181&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8299713
  Stats: 64 lines in 1 file changed: 40 ins; 5 del; 19 mod
  Patch: https://git.openjdk.org/jdk/pull/12181.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/12181/head:pull/12181

PR: https://git.openjdk.org/jdk/pull/12181