backend/tests: add objectExpression{1,2,3}

backend.native/tests/codegen/objectExpression/1.kt

@@ -0,0 +1,13 @@
+fun main(args: Array<String>) {
+    val a = "a"
+
+    val x = object {
+        override fun toString(): String {
+            return foo(a) + foo("b")
+        }
+
+        fun foo(s: String) = s + s
+    }
+
+    println(x.toString())
+}