codeql-go merge prep: move into go/ directory

go/extractor/net/sourceforge/pmd/cpd/SourceCode.java

@@ -0,0 +1,12 @@
+package net.sourceforge.pmd.cpd;
+
+/*
+ * This is a stub definition for pmd's SourceCode class
+ * including only the API used by the GoLanguage class.
+ */
+
+public class SourceCode {
+  public String getFileName() {
+    return null;
+  }
+}