Map proper owner for method with default args

compiler/testData/codegen/java8/box/jvm8/defaultArgs.kt

@@ -0,0 +1,13 @@
+// JVM_TARGET: 1.8
+
+interface Z {
+    fun test(s: String = "OK"): String {
+        return s
+    }
+}
+
+class Test: Z
+
+fun box(): String {
+    return Test().test()
+}