Prohibit nested intersection types in return position

#KT-11490 Fixed

compiler/testData/diagnostics/tests/implicitNestedIntersection.kt

@@ -0,0 +1,9 @@
+// !DIAGNOSTICS: -UNUSED_PARAMETER
+
+interface In<in E>
+open class A : In<A>
+open class B : In<B>
+
+fun <T> select(x: T, y: T) = x
+
+fun <!IMPLICIT_INTERSECTION_TYPE!>foo2<!>() = select(A(), B()) // Type is In<A & B> is prohibited in return position