Update Java linters and fix new PMD errors (#4157)

PMD requires that variables only initialized in the constructor be
final. The compiler errors if those final variables aren't guaranteed to
be initialized, so extra else branches were added to ensure that.

PMD also requires that classes with only private constructors be final.
The equivalent C++ classes were finalized as well, except for
TimeInterpolatableBuffer because it doesn't expose factory functions.

wpilibc/src/main/native/include/frc/DriverStation.h

@@ -19,7 +19,7 @@ namespace frc {
  * Provide access to the network communication data to / from the Driver
  * Station.
  */
-class DriverStation {
+class DriverStation final {
  public:
   enum Alliance { kRed, kBlue, kInvalid };
   enum MatchType { kNone, kPractice, kQualification, kElimination };

wpilibc/src/main/native/include/frc/livewindow/LiveWindow.h

@@ -18,7 +18,7 @@ namespace frc {
  * The LiveWindow class is the public interface for putting sensors and
  * actuators on the LiveWindow.
  */
-class LiveWindow {
+class LiveWindow final {
  public:
   /**
    * Get an instance of the LiveWindow main class.