Split online.cs and offline.csFile (#941)

Co-authored-by: 东风破 <birdfishs@163.com>

scripts/dotnet/OfflineTtsModelConfig.cs

@@ -0,0 +1,29 @@
+/// Copyright (c)  2024.5 by 东风破
+
+using System.Linq;
+using System.Collections.Generic;
+using System.Runtime.InteropServices;
+using System.Text;
+using System;
+
+namespace SherpaOnnx
+{
+
+    [StructLayout(LayoutKind.Sequential)]
+    public struct OfflineTtsModelConfig
+    {
+        public OfflineTtsModelConfig()
+        {
+            Vits = new OfflineTtsVitsModelConfig();
+            NumThreads = 1;
+            Debug = 0;
+            Provider = "cpu";
+        }
+
+        public OfflineTtsVitsModelConfig Vits;
+        public int NumThreads;
+        public int Debug;
+        [MarshalAs(UnmanagedType.LPStr)]
+        public string Provider;
+    }
+}