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"
+}

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"
+}

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

@@ -0,0 +1,28 @@
+var result = ""
+
+trait D1 {
+    fun foo(): D1 {
+        result += "D1"
+        return this
+    }
+}
+
+trait F2 : D1
+
+trait D3 : F2 {
+    override fun foo(): D3 {
+        result += "D3"
+        return this
+    }
+}
+
+class D4 : D3
+
+fun box(): String {
+    val x = D4()
+    x.foo()
+    (x : D3).foo()
+    (x : F2).foo()
+    (x : D1).foo()
+    return if (result == "D3D3D3D3") "OK" else "Fail: $result"
+}

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

@@ -0,0 +1,25 @@
+trait D1 {
+    fun foo(): Any
+}
+
+trait D2 {
+    fun foo(): Number
+}
+
+trait F3 : D1, D2
+
+open class D4 {
+    fun foo(): Int = 42
+}
+
+class F5 : F3, D4()
+
+fun box(): String {
+    val z = F5()
+    var result = z.foo()
+    result += (z : D4).foo()
+    result += (z : F3).foo() as Int
+    result += (z : D2).foo() as Int
+    result += (z : D1).foo() as Int
+    return if (result == 5 * 42) "OK" else "Fail: $result"
+}