RFR: 8329559: Test javax/swing/JFrame/bug4419914.java failed because The End and Start buttons are not placed correctly and Tab focus does not move as expected

[Prasanta Sadhukhan]

Test issue shows the End and Start buttons are not placed as per instructions due to ComponentOrientation RTL was not honoured, as with `getContentPane()` being removed from `add` call of JFrame, it was also additionally removed from other JFrame calls which resulted in the RTL not being propagated to its child. Fix is to add `getContentPane()` to the non-add methods of JFrame as was done in the applet version of the test..

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Commit messages:
 - 8329559: Test javax/swing/JFrame/bug4419914.java failed because The End and Start buttons are not placed correctly and Tab focus does not move as expected

Changes: https://git.openjdk.org/jdk/pull/18612/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=18612&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8329559
  Stats: 6 lines in 1 file changed: 2 ins; 1 del; 3 mod
  Patch: https://git.openjdk.org/jdk/pull/18612.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/18612/head:pull/18612

PR: https://git.openjdk.org/jdk/pull/18612