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

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

scripts/dotnet/OfflineTtsGeneratedAudio.cs

@@ -0,0 +1,93 @@
+/// 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
+{
+    public class OfflineTtsGeneratedAudio
+    {
+        public OfflineTtsGeneratedAudio(IntPtr p)
+        {
+            _handle = new HandleRef(this, p);
+        }
+
+        public bool SaveToWaveFile(String filename)
+        {
+            Impl impl = (Impl)Marshal.PtrToStructure(Handle, typeof(Impl));
+            int status = SherpaOnnxWriteWave(impl.Samples, impl.NumSamples, impl.SampleRate, filename);
+            return status == 1;
+        }
+
+        ~OfflineTtsGeneratedAudio()
+        {
+            Cleanup();
+        }
+
+        public void Dispose()
+        {
+            Cleanup();
+            // Prevent the object from being placed on the
+            // finalization queue
+            System.GC.SuppressFinalize(this);
+        }
+
+        private void Cleanup()
+        {
+            SherpaOnnxDestroyOfflineTtsGeneratedAudio(Handle);
+
+            // Don't permit the handle to be used again.
+            _handle = new HandleRef(this, IntPtr.Zero);
+        }
+
+        [StructLayout(LayoutKind.Sequential)]
+        struct Impl
+        {
+            public IntPtr Samples;
+            public int NumSamples;
+            public int SampleRate;
+        }
+
+        private HandleRef _handle;
+        public IntPtr Handle => _handle.Handle;
+
+        public int NumSamples
+        {
+            get
+            {
+                Impl impl = (Impl)Marshal.PtrToStructure(Handle, typeof(Impl));
+                return impl.NumSamples;
+            }
+        }
+
+        public int SampleRate
+        {
+            get
+            {
+                Impl impl = (Impl)Marshal.PtrToStructure(Handle, typeof(Impl));
+                return impl.SampleRate;
+            }
+        }
+
+        public float[] Samples
+        {
+            get
+            {
+                Impl impl = (Impl)Marshal.PtrToStructure(Handle, typeof(Impl));
+
+                float[] samples = new float[impl.NumSamples];
+                Marshal.Copy(impl.Samples, samples, 0, impl.NumSamples);
+                return samples;
+            }
+        }
+
+        [DllImport(Dll.Filename)]
+        private static extern void SherpaOnnxDestroyOfflineTtsGeneratedAudio(IntPtr handle);
+
+        [DllImport(Dll.Filename)]
+        private static extern int SherpaOnnxWriteWave(IntPtr samples, int n, int sample_rate, [MarshalAs(UnmanagedType.LPStr)] string filename);
+    }
+}