j2k: flatten test cases and testData directory structure

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

j2k/testData/fileOrElement/enum/enumWithNameField.kt

@@ -0,0 +1,5 @@
+enum class E {
+    I
+
+    private val name: String? = null
+}