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.

hal/src/generate/FRCNetComm.java.in

@@ -12,7 +12,7 @@ public class FRCNetComm {
   /**
    * Resource type from UsageReporting.
    */
-  @SuppressWarnings({"TypeName", "PMD.ConstantsInInterface"})
+  @SuppressWarnings("TypeName")
   public static final class tResourceType {
     private tResourceType() {
     }
@@ -23,7 +23,7 @@ ${usage_reporting_types}
   /**
    * Instances from UsageReporting.
    */
-  @SuppressWarnings({"TypeName", "PMD.ConstantsInInterface"})
+  @SuppressWarnings("TypeName")
   public static final class tInstances {
     private tInstances() {
     }