Add partition by file size (#497)

DiscordChatExporter.Gui/Utils/PartitionFormat.cs

@@ -0,0 +1,22 @@
+using System;
+using System.Collections.Generic;
+using System.Text;
+
+namespace DiscordChatExporter.Gui.Internal
+{
+    public enum PartitionFormat
+    {
+        MessageCount,
+        FileSize,
+    }
+
+    public static class PartitionFormatExtensions
+    {
+        public static string GetDisplayName(this PartitionFormat format) => format switch
+        {
+            PartitionFormat.MessageCount => "Message count",
+            PartitionFormat.FileSize => "File size (MB)",
+            _ => throw new ArgumentOutOfRangeException(nameof(format))
+        };
+    }
+}