Test TypeAs expression is always not lifted.

Commit migrated from https://github.com/dotnet/corefx/commit/76fbb895c4e350566fabbe29ec316ab8d2aced8e

src/libraries/System.Linq.Expressions/tests/Cast/AsNullable.cs

@@ -10,6 +10,13 @@ namespace System.Linq.Expressions.Tests
 {
     public static class AsNullableTests
     {
+        [Fact]
+        public static void NotLiftedEvenOnNullableOperandOrType()
+        {
+            Assert.False(Expression.TypeAs(Expression.Constant(E.A, typeof(E?)), typeof(E?)).IsLifted);
+            Assert.False(Expression.TypeAs(Expression.Constant(E.A, typeof(E?)), typeof(Enum)).IsLifted);
+        }
+
         #region Test methods
 
         [Theory, ClassData(typeof(CompilationTypes))]