Allow bare types on the right-hand side of as/as?/is/!is

compiler/testData/diagnostics/tests/cast/bare/EitherWhen.kt

@@ -0,0 +1,18 @@
+trait Either<out A, out B>
+trait Left<out A>: Either<A, Nothing> {
+    val value: A
+}
+trait Right<out B>: Either<Nothing, B> {
+    val value: B
+}
+
+class C1(val v1: Int)
+class C2(val v2: Int)
+
+fun _when(e: Either<C1, C2>): Any {
+    return when (e) {
+        is Left -> e.value.v1
+        is Right -> e.value.v2
+        else -> e
+    }
+}