Generate bridges for fake overrides when needed

#KT-3985 Fixed
 #KT-4145 Fixed

compiler/testData/codegen/box/bridges/simpleTraitImpl.kt

@@ -0,0 +1,15 @@
+trait A<T> {
+    fun foo(t: T) = "A"
+}
+
+class Z : A<String>
+
+
+fun box(): String {
+    val z = Z()
+    return when {
+        z.foo("")               != "A" -> "Fail #1"
+        (z : A<String>).foo("") != "A" -> "Fail #2"
+        else -> "OK"
+    }
+}