Java: add extractor diagnostic queries

java/ql/src/Diagnostics/SuccessfullyExtractedFiles.ql

@@ -0,0 +1,14 @@
+/**
+ * @name Successfully extracted files
+ * @description A list of all files in the source code directory that
+ *              were extracted without encountering an error in the file.
+ * @kind diagnostic
+ * @id java/diagnostics/successfully-extracted-files
+ */
+
+import java
+import DiagnosticsReporting
+
+from CompilationUnit f
+where successfullyExtracted(f)
+select f, ""