j2k: flatten test cases and testData directory structure

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

j2k/testData/fileOrElement/callChainExpression/libraryMethodCall.java

@@ -0,0 +1,12 @@
+class Library {
+  static void call() {}
+
+  static String getString() { return ""; }
+}
+
+class User {
+  void main() {
+    Library.call();
+    Library.getString().isEmpty();
+  }
+}