j2k: flatten test cases and testData directory structure

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

j2k/testData/fileOrElement/trait/interfaceWithStaticFields.kt

@@ -0,0 +1,7 @@
+public trait INode {
+    class object {
+        public val IN: String = "in"
+        public val AT: String = "@"
+        public val COMMA_WITH_SPACE: String = COMMA + SPACE
+    }
+}