- change ModifyDialog.FocusManager.changeFont() method to
  add DisposeListener to the control to dispose of the new
  Font created

Change-Id: Ia0d0dd0c97604803692522d78b008e12c0a7fb30
Reviewed-on: https://git.eclipse.org/r/c/jdt/eclipse.jdt.ui/+/182479
Reviewed-by: Andrey Loskutov <loskutov@gmx.de>
Reviewed-by: Jeff Johnston <jjohnstn@redhat.com>
Tested-by: JDT Bot <jdt-bot@eclipse.org>