RFR: 6753661: JFileChooser font not reset after Look & Feel change

[Prasanta Sadhukhan]

Issue is observed that after changing the Look & Feel from Metal to Nimbus and back to Metal, the Nimbus font continues to be used by a JFileChooser.
This is because Synth  `installDefaults `methods set the font, but its inverse methods `uninstallDefaults `do not remove them.
Fix is made to reset the font if it is set by L&F.

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Commit messages:
 - 6753661: JFileChooser font not reset after Look & Feel change

Changes: https://git.openjdk.org/jdk/pull/12180/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=12180&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-6753661
  Stats: 55 lines in 2 files changed: 55 ins; 0 del; 0 mod
  Patch: https://git.openjdk.org/jdk/pull/12180.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/12180/head:pull/12180

PR: https://git.openjdk.org/jdk/pull/12180