Added tests on bridges

backend.native/tests/codegen/bridges/test16.kt

@@ -0,0 +1,20 @@
+interface A {
+    fun foo(): String
+}
+
+abstract class C: A
+
+open class B: C() {
+    override fun foo(): String {
+        return "OK"
+    }
+}
+
+fun bar(c: C) = c.foo()
+
+fun main(args: Array<String>) {
+    val b = B()
+    val c: C = b
+    println(bar(b))
+    println(bar(c))
+}