j2k: flatten test cases and testData directory structure

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

j2k/testData/fileOrElement/toKotlinClasses/iterableAndIterator.kt

@@ -0,0 +1,25 @@
+// ERROR: Null can not be a value of a non-null type kotlin.Iterator<kotlin.String>
+// ERROR: Null can not be a value of a non-null type kotlin.Iterator<kotlin.String>
+package demo
+
+class Test : Iterable<String> {
+    override fun iterator(): Iterator<String> {
+        return null
+    }
+
+    public fun push(i: Iterator<String>): Iterator<String> {
+        val j = i
+        return j
+    }
+}
+
+class FullTest : Iterable<String> {
+    override fun iterator(): Iterator<String> {
+        return null
+    }
+
+    public fun push(i: Iterator<String>): Iterator<String> {
+        val j = i
+        return j
+    }
+}