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.

wpiutil/src/main/java/edu/wpi/first/wpiutil/CombinedRuntimeLoader.java

@@ -56,11 +56,7 @@ public final class CombinedRuntimeLoader {
    * @return List of all libraries that were extracted
    * @throws IOException Thrown if resource not found or file could not be extracted
    */
-  @SuppressWarnings({
-    "PMD.AvoidInstantiatingObjectsInLoops",
-    "PMD.UnnecessaryCastRule",
-    "unchecked"
-  })
+  @SuppressWarnings({"PMD.UnnecessaryCastRule", "unchecked"})
   public static <T> List<String> extractLibraries(Class<T> clazz, String resourceName)
       throws IOException {
     TypeReference<HashMap<String, Object>> typeRef =

wpiutil/src/main/java/edu/wpi/first/wpiutil/RuntimeDetector.java

@@ -15,7 +15,6 @@ public final class RuntimeDetector {
   private static String fileExtension;
   private static String filePath;
 
-  @SuppressWarnings("PMD.CyclomaticComplexity")
   private static synchronized void computePlatform() {
     if (fileExtension != null && filePath != null && filePrefix != null) {
       return;

wpiutil/src/main/java/edu/wpi/first/wpiutil/RuntimeLoader.java

@@ -107,13 +107,7 @@ public final class RuntimeLoader<T> {
   }
 
   /** Load a native library by directly hashing the file. */
-  @SuppressWarnings({
-    "PMD.NPathComplexity",
-    "PMD.PreserveStackTrace",
-    "PMD.EmptyWhileStmt",
-    "PMD.AvoidThrowingRawExceptionTypes",
-    "PMD.CyclomaticComplexity"
-  })
+  @SuppressWarnings({"PMD.PreserveStackTrace", "PMD.EmptyWhileStmt"})
   public void loadLibraryHashed() throws IOException {
     try {
       // First, try loading path