[csharp-netcore] Enum parameter serialization to use EnumMember value…

… when provided. (OpenAPITools#11448)

* Add modification to petstore yaml to support testing enum string resolve. Move csharp-netcore-net50 to point to new yaml schema.

* [csharp-netcore] - For enum's with an EnumMember Attribute use this value instead of enum.ToString().

-Regenerate csharp samples to accomodate change.

* fix: rebase on master.  Update samples.

* task (Samples): update csharp-netcore samples. (via generate-samples.sh)

modules/openapi-generator/src/main/resources/csharp-netcore/ClientUtils.mustache

@@ -5,6 +5,7 @@ using System.Collections;
 using System.Globalization;
 using System.IO;
 using System.Linq;
+using System.Runtime.Serialization;
 using System.Text;
 using System.Text.RegularExpressions;
 {{#useCompareNetObjects}}
@@ -112,6 +113,8 @@ namespace {{packageName}}.Client
                 return boolean ? "true" : "false";
             if (obj is ICollection collection)
                 return string.Join(",", collection.Cast<object>());
+            if (obj is Enum && HasEnumMemberAttrValue(obj))
+                return GetEnumMemberAttrValue(obj);
 
             return Convert.ToString(obj, CultureInfo.InvariantCulture);
         }
@@ -210,5 +213,40 @@ namespace {{packageName}}.Client
 
             return JsonRegex.IsMatch(mime) || mime.Equals("application/json-patch+json");
         }
+
+        /// <summary>
+        /// Is the Enum decorated with EnumMember Attribute
+        /// </summary>
+        /// <param name="enumVal"></param>
+        /// <returns>true if found</returns>
+        private static bool HasEnumMemberAttrValue(object enumVal)
+        {
+            if (enumVal == null)
+                throw new ArgumentNullException(nameof(enumVal));
+            var enumType = enumVal.GetType();
+            var memInfo = enumType.GetMember(enumVal.ToString() ?? throw new InvalidOperationException());
+            var attr = memInfo.FirstOrDefault()?.GetCustomAttributes(false).OfType<EnumMemberAttribute>().FirstOrDefault();
+            if (attr != null) return true;
+                return false;
+        }
+
+        /// <summary>
+        /// Get the EnumMember value
+        /// </summary>
+        /// <param name="enumVal"></param>
+        /// <returns>EnumMember value as string otherwise null</returns>
+        private static string GetEnumMemberAttrValue(object enumVal)
+        {
+            if (enumVal == null)
+                throw new ArgumentNullException(nameof(enumVal));
+            var enumType = enumVal.GetType();
+            var memInfo = enumType.GetMember(enumVal.ToString() ?? throw new InvalidOperationException());
+            var attr = memInfo.FirstOrDefault()?.GetCustomAttributes(false).OfType<EnumMemberAttribute>().FirstOrDefault();
+            if (attr != null)
+            {
+                return attr.Value;
+            }
+            return null;
+        }
     }
 }