String content emoji (#11386)

Test fix of high-ascii encoding.

src/Mvc/Mvc.ViewFeatures/test/StringHtmlContentTest.cs

@@ -2,6 +2,7 @@
 // Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.
 
 using System.IO;
+using System.Text.Encodings.Web;
 using Microsoft.Extensions.WebEncoders.Testing;
 using Xunit;
 
@@ -22,5 +23,19 @@ namespace Microsoft.AspNetCore.Mvc.ViewFeatures
                 Assert.Equal("HtmlEncode[[Hello World]]", writer.ToString());
             }
         }
+
+        [Fact]
+        public void Emoji_EncodedCorrectly()
+        {
+            // Arrange & Act
+            var tearsOfJoy = new StringHtmlContent("😂2");
+
+            // Assert
+            using (var stringWriter = new StringWriter())
+            {
+                tearsOfJoy.WriteTo(stringWriter, HtmlEncoder.Default);
+                Assert.Equal("😂2", stringWriter.ToString(), ignoreCase: true);
+            }
+        }
     }
 }