fix: avoid NPE from Auxiliary.class.getPackage() on JDK 8

On JDK 8, Class.getPackage() returns null for classes dynamically
defined on the bootstrap classloader because the VM package table is
only populated for file-loaded classes. Derive the package path from
Class.getName() instead.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: jbachorik

btrace-instr/src/test/java/org/openjdk/btrace/instr/InstrumentorTestBase.java

@@ -202,7 +202,7 @@ public void visit(
                           String[] interfaces) {
                     int idx = name.lastIndexOf('/');
                     name =
-                            Auxiliary.class.getPackage().getName().replace('.', '/')
+                            Auxiliary.class.getName().substring(0, Auxiliary.class.getName().lastIndexOf('.')).replace('.', '/')
                                     + '/'
                                     + name.substring(idx + 1);
                     super.visit(version, access, name, signature, superName, interfaces);

btrace-runtime/src/main/java/org/openjdk/btrace/runtime/BTraceRuntimeAccessImpl.java

@@ -43,6 +43,15 @@
 public final class BTraceRuntimeAccessImpl implements BTraceRuntimeAccess.Delegate {
   private static final BTraceRuntimeAccessImpl INSTANCE = new BTraceRuntimeAccessImpl();
 
+  // Auxiliary.class.getPackage() returns null on JDK 8 when the class is dynamically defined
+  // on the bootstrap classloader (the VM package table is only populated for file-loaded classes)
+  private static final String AUXILIARY_PKG;
+
+  static {
+    String name = Auxiliary.class.getName();
+    AUXILIARY_PKG = name.substring(0, name.lastIndexOf('.')).replace('.', '/');
+  }
+
   static final class RTWrapper {
     private BTraceRuntime.Impl rt = null;
 
@@ -140,11 +149,11 @@ static String getClientNameInternal(String forClassName) {
     int idx = forClassName.lastIndexOf('/');
     if (idx > -1) {
       forClassName =
-          Auxiliary.class.getPackage().getName().replace('.', '/')
+          AUXILIARY_PKG
               + "/"
               + forClassName.substring(idx + 1);
     } else {
-      forClassName = Auxiliary.class.getPackage().getName().replace('.', '/') + "/" + forClassName;
+      forClassName = AUXILIARY_PKG + "/" + forClassName;
     }
 
     if (!BTraceRuntimeAccess.isUniqueClientClassNames()) {