Add proper support for more system notifications

Closes #844

DiscordChatExporter.Core/Utils/Extensions/StringExtensions.cs

@@ -1,7 +1,6 @@
 using System;
 using System.Collections.Generic;
 using System.Text;
-using System.Text.RegularExpressions;
 
 namespace DiscordChatExporter.Core.Utils.Extensions;
 
@@ -27,9 +26,6 @@ public static class StringExtensions
         }
     }
 
-    public static string ToDashCase(this string str) =>
-        Regex.Replace(str, @"(\p{Ll})(\p{Lu})", "$1-$2");
-
     public static T? ParseEnumOrNull<T>(this string str, bool ignoreCase = true) where T : struct, Enum =>
         Enum.TryParse<T>(str, ignoreCase, out var result)
             ? result