Generate bridges for fake overrides when needed

#KT-3985 Fixed
 #KT-4145 Fixed

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

@@ -0,0 +1,21 @@
+// KT-3985
+
+trait Trait<T> {
+    fun f(): T
+}
+
+open class Class {
+    fun f(): String = throw UnsupportedOperationException()
+}
+
+class Foo: Class(), Trait<String> {
+}
+
+fun box(): String {
+    try {
+        (Foo() : Trait<String>).f()
+    } catch (e: UnsupportedOperationException) {
+        return "OK"
+    }
+    return "Fail"
+}