[dotnet] Optimize reflection in JsonEnumMemberConverter (#15205)

Author: RenderMichael

dotnet/src/webdriver/DevTools/Json/JsonEnumMemberConverter.cs

@@ -26,19 +26,23 @@
 
 namespace OpenQA.Selenium.DevTools.Json
 {
-    internal class JsonEnumMemberConverter<TEnum> : JsonConverter<TEnum> where TEnum : Enum
+    internal sealed class JsonEnumMemberConverter<TEnum> : JsonConverter<TEnum>
+        where TEnum : struct, Enum
     {
         private readonly Dictionary<TEnum, string> _enumToString = new Dictionary<TEnum, string>();
         private readonly Dictionary<string, TEnum> _stringToEnum = new Dictionary<string, TEnum>();
 
         public JsonEnumMemberConverter()
         {
             var type = typeof(TEnum);
-            var values = Enum.GetValues(type);
-
+#if NET8_0_OR_GREATER
+            TEnum[] values = Enum.GetValues<TEnum>();
+#else
+            Array values = Enum.GetValues(type);
+#endif
             foreach (var value in values)
             {
-                var enumMember = type.GetMember(value.ToString())[0];
+                var enumMember = type.GetField(value.ToString());
                 var attr = enumMember.GetCustomAttributes(typeof(EnumMemberAttribute), false)
                   .Cast<EnumMemberAttribute>()
                   .FirstOrDefault();