Disable frivolous PMD warnings and enable PMD in ntcore (#3419)

Some valid warnings like throwing NullPointerException or using a for
loop instead of System.arraycopy() were fixed.

Abstract classes marked with PMD.AbstractClassWithoutAbstractMethod were
made concrete because they already had protected constructors.

Fixes #1697.

wpimath/src/test/java/edu/wpi/first/math/controller/LinearSystemLoopTest.java

@@ -52,7 +52,7 @@ public class LinearSystemLoopTest {
   }
 
   @Test
-  @SuppressWarnings({"LocalVariableName", "PMD.AvoidInstantiatingObjectsInLoops"})
+  @SuppressWarnings("LocalVariableName")
   public void testStateSpaceEnabled() {
 
     m_loop.reset(VecBuilder.fill(0, 0));
@@ -82,7 +82,7 @@ public class LinearSystemLoopTest {
   }
 
   @Test
-  @SuppressWarnings({"LocalVariableName", "PMD.AvoidInstantiatingObjectsInLoops"})
+  @SuppressWarnings("LocalVariableName")
   public void testFlywheelEnabled() {
 
     LinearSystem<N1, N1, N1> plant =

wpimath/src/test/java/edu/wpi/first/math/controller/RamseteControllerTest.java

@@ -21,7 +21,6 @@ class RamseteControllerTest {
   private static final double kAngularTolerance = Math.toRadians(2);
 
   @Test
-  @SuppressWarnings("PMD.AvoidInstantiatingObjectsInLoops")
   void testReachesReference() {
     final var controller = new RamseteController(2.0, 0.7);
     var robotPose = new Pose2d(2.7, 23.0, Rotation2d.fromDegrees(0.0));