RFR: 8346055: javax/swing/text/StyledEditorKit/4506788/bug4506788.java fails in ubuntu22.04

[Prasanta Sadhukhan]

javax/swing/text/StyledEditorKit/4506788/bug4506788.java fails in ubuntu22.04 seems to fail in OCI system citing "Test failed"
suggesting caret is not at expected place after text is typed, but I could not find any CI jobs having it failed.
Anyway simplified the test and added stability fixes which made it pass now in several OCI systems..

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Commit messages:
 - jcheck
 - testfix

Changes: https://git.openjdk.org/jdk/pull/22698/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=22698&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8346055
  Stats: 80 lines in 1 file changed: 18 ins; 40 del; 22 mod
  Patch: https://git.openjdk.org/jdk/pull/22698.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/22698/head:pull/22698

PR: https://git.openjdk.org/jdk/pull/22698