j2k: flatten test cases and testData directory structure

Move j2k/test/tests -> j2k/tests, j2k/test/testData -> j2k/testData

j2k/testData/fileOrElement/mutableCollections/FunctionParameters2.java

@@ -0,0 +1,11 @@
+import java.util.*;
+
+class A {
+    void foo(Set<String> set) {
+        bar(set);
+    }
+
+    void bar(Collection<String> collection) {
+        collection.add("a");
+    }
+}