Add normalization; use constant for Examples extension

Author: MaggieKimani1

src/Microsoft.OpenApi.Readers/V2/OpenApiResponseDeserializer.cs

@@ -42,7 +42,7 @@ internal static partial class OpenApiV2Deserializer
         private static readonly PatternFieldMap<OpenApiResponse> _responsePatternFields =
             new()
             {
-                {s => s.StartsWith("x-") && !s.Equals("x-examples", StringComparison.OrdinalIgnoreCase), (o, p, n) => o.AddExtension(p, LoadExtension(p, n))}
+                {s => s.StartsWith("x-") && !s.Equals(OpenApiConstants.ExamplesExtension), (o, p, n) => o.AddExtension(p, LoadExtension(p, n))}
             };
 
         private static readonly AnyFieldMap<OpenApiMediaType> _mediaTypeAnyFields =
@@ -106,7 +106,7 @@ private static void ProcessProduces(MapNode mapNode, OpenApiResponse response, P
 
         private static void LoadExamplesExtension(OpenApiResponse response, ParseNode node)
         {
-            var mapNode = node.CheckMapNode("x-examples");
+            var mapNode = node.CheckMapNode(OpenApiConstants.ExamplesExtension);
             var examples = new Dictionary<string, OpenApiExample>();
 
             foreach (var examplesNode in mapNode)
@@ -116,7 +116,7 @@ private static void LoadExamplesExtension(OpenApiResponse response, ParseNode no
                 var exampleNode = examplesNode.Value.CheckMapNode(examplesNode.Name);
                 foreach (var valueNode in exampleNode)
                 {
-                    switch (valueNode.Name)
+                    switch (valueNode.Name.ToLowerInvariant())
                     {
                         case "summary":
                             example.Summary = valueNode.Value.GetScalarValue();

src/Microsoft.OpenApi/Models/OpenApiConstants.cs

@@ -565,6 +565,11 @@ public static class OpenApiConstants
         /// </summary>
         public const string BodyName = "x-bodyName";
 
+        /// <summary>
+        /// Field: Examples Extension
+        /// </summary>
+        public const string ExamplesExtension = "x-examples";
+
         /// <summary>
         /// Field: version3_0_0
         /// </summary>

src/Microsoft.OpenApi/Models/OpenApiParameter.cs

@@ -390,7 +390,7 @@ public void SerializeAsV2WithoutReference(IOpenApiWriter writer)
             //examples
             if (Examples != null && Examples.Any())
             {
-                writer.WritePropertyName("x-examples");
+                writer.WritePropertyName(OpenApiConstants.ExamplesExtension);
                 writer.WriteStartObject();
 
                 foreach (var example in Examples)

src/Microsoft.OpenApi/Models/OpenApiResponse.cs

@@ -196,7 +196,7 @@ public void SerializeAsV2WithoutReference(IOpenApiWriter writer)
 
                     if (Content.Values.Any(m => m.Examples != null && m.Examples.Any()))
                     {
-                        writer.WritePropertyName("x-examples");
+                        writer.WritePropertyName(OpenApiConstants.ExamplesExtension);
                         writer.WriteStartObject();
 
                         foreach (var example in Content