j2k: flatten test cases and testData directory structure

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

j2k/testData/fileOrElement/nullability/MethodResultComparedWithNull4.kt

@@ -0,0 +1,13 @@
+trait I {
+    public fun getString(): String
+}
+
+class C {
+    fun foo(i: I, b: Boolean) {
+        var result: String? = i.getString()
+        if (b) result = null
+        if (result != null) {
+            print(result)
+        }
+    }
+}