j2k: flatten test cases and testData directory structure

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

j2k/testData/fileOrElement/constructors/fieldsInitializedFromParams7.kt

@@ -0,0 +1,10 @@
+// ERROR: Property must be initialized or be abstract
+class C(x: Any, b: Boolean) {
+    public var x: Any
+
+    {
+        if (b) {
+            this.x = x
+        }
+    }
+}