Generate bridges for fake overrides when needed

#KT-3985 Fixed
 #KT-4145 Fixed

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

@@ -0,0 +1,19 @@
+// KT-4145
+
+trait A {
+    fun foo(): Any
+}
+
+open class B {
+    fun foo(): String = "A"
+}
+
+open class C: B(), A
+
+fun box(): String {
+    val a: A = C()
+    if (a.foo() != "A") return "Fail 1"
+    if ((a as B).foo() != "A") return "Fail 2"
+    if ((a as C).foo() != "A") return "Fail 3"
+    return "OK"
+}