backend/tests: add disabled test 'fields2'

Checks properties with custom accessors and backing fields.

backend.native/tests/codegen/object/fields2.kt

@@ -0,0 +1,31 @@
+var global: Int = 0
+    get() {
+        println("Get global = $field")
+        return field
+    }
+    set(value) {
+        println("Set global = $value")
+        field = value
+    }
+
+class Test {
+    var member: Int = 0
+        get() {
+            println("Get member = $field")
+            return field
+        }
+        set(value) {
+            println("Set member = $value")
+            field = value
+        }
+}
+
+fun main(args:Array<String>) {
+    global = 1
+
+    val test = Test()
+    test.member = 42
+
+    global = test.member
+    test.member = global
+}