RFR: 6726690: SwingUtilities.replaceUI*Map() methods do not remove previously installed maps

[Prasanta Sadhukhan]

`SwingUtilities.replaceUIInputMap()` and `SwingUtilities.replaceUIActionMap()` do not actually remove previously installed maps as their Javadoc indicates if `null` is passed as argument to `uiInputMap`/`uiActionMap`

https://github.com/openjdk/jdk/blob/7e91d34f3e83b4c39d6ce5de34373d7d74d54512/src/java.desktop/share/classes/javax/swing/SwingUtilities.java#L1802-L1803
https://github.com/openjdk/jdk/blob/7e91d34f3e83b4c39d6ce5de34373d7d74d54512/src/java.desktop/share/classes/javax/swing/SwingUtilities.java#L1827-L1828

If the passed  `uiInputMap`/`uiActionMap` is null, `JComponent` actually doesn't create a fresh map and returns the previously installed map 
https://github.com/openjdk/jdk/blob/7e91d34f3e83b4c39d6ce5de34373d7d74d54512/src/java.desktop/share/classes/javax/swing/JComponent.java#L2586-L2595
which is in contradiction to the `replaceUI*Map` spec so `SwingUtilities `needs to clear the previously installed map which is being done in this fix.

-------------

Commit messages:
 - Test fix
 - Test fix
 - 6726690: SwingUtilities.replaceUI*Map() methods do not remove previously installed maps

Changes: https://git.openjdk.org/jdk/pull/28671/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=28671&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-6726690
  Stats: 78 lines in 2 files changed: 78 ins; 0 del; 0 mod
  Patch: https://git.openjdk.org/jdk/pull/28671.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/28671/head:pull/28671

PR: https://git.openjdk.org/jdk/pull/28671