j2k: flatten test cases and testData directory structure

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

j2k/testData/fileOrElement/issues/kt-543-boxed.java

@@ -0,0 +1,14 @@
+//file
+package demo;
+
+class Test {
+  void putInt(Integer i) {}
+
+  void test() {
+    byte b = 10;
+    putInt(b);
+
+    Byte b2 = 10;
+    putInt(b2);
+  }
+}