Fix common supertype calculation

Use star-projections instead of 'out Any?' in corner cases

 #KT-11468 Fixed

compiler/testData/codegen/box/regressions/commonSupertypeContravariant.kt

@@ -0,0 +1,11 @@
+interface In<in E>
+
+class En<T> : In<T>
+class A : In<A>
+fun <T> select(x: T, y: T): T = x ?: y
+
+// This test just checks that no internal error happens in backend
+// Return type should be In<*> nor In<out Any?>
+fun foobar(e: En<*>) = select(A(), e)
+
+fun box() = "OK"

compiler/testData/codegen/box/regressions/commonSupertypeContravariant2.kt

@@ -0,0 +1,9 @@
+interface In<in E>
+class A : In<A>
+class B : In<B>
+fun <T> select(x: T, y: T) = x ?: y
+
+// This test just checks that no internal error happens in backend
+fun foobar(a: A, b: B) = select(a, b)
+
+fun box() = "OK"