Java 21 (LTS) support

[gituser789]

Thanks for providing the adapted gecko version! I am using this since a few years now to automate simulations.

After switching to a new java-version using archlinux-java set java-21-openjdk, the following failure is raised when controlling gecko via python.

    self.ginst = self.Inst.startNewRemoteInstance(self.geckoport)
                 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "jnius/jnius_export_class.pxi", line 1163, in jnius.JavaMultipleMethod.__call__
  File "jnius/jnius_export_class.pxi", line 876, in jnius.JavaMethod.__call__
  File "jnius/jnius_export_class.pxi", line 1042, in jnius.JavaMethod.call_staticmethod
  File "jnius/jnius_utils.pxi", line 79, in jnius.check_exception
jnius.JavaException: JVM exception occurred: java.lang.UnsupportedOperationException

When i switch back archlinux-java set java-17-openjdk, the python code interface works fine.

Are there any plans to upgrade this gecko build for the latest java LTS in future?