Don't allow fake override to inherit implementation with wrong return type

#KT-4763 Fixed

idea/testData/diagnosticMessage/wrongReturnTypeInImplementation.kt

@@ -0,0 +1,27 @@
+// !DIAGNOSTICS_NUMBER: 1
+// !DIAGNOSTICS: ABSTRACT_MEMBER_NOT_IMPLEMENTED
+// !MESSAGE_TYPE: TEXT
+
+trait T1
+trait T2 : T1
+trait T3 : T2
+trait T4 : T3
+
+
+trait A {
+    fun f(): T1
+}
+
+trait B {
+    fun f(): T2 = null!!
+}
+
+trait C {
+    fun f(): T3
+}
+
+abstract class D {
+    abstract fun f(): T4
+}
+
+class E : A, B, C, D()

idea/testData/diagnosticMessage/wrongReturnTypeInImplementation1.txt

@@ -0,0 +1,2 @@
+<!-- wrongReturnTypeInImplementation1 -->
+Class 'E' must be declared abstract or implement abstract member internal abstract fun f(): T3 defined in C