added ClipboardImpl with hooks to navigator.clipboard.readtext and naviagot.clipboard.writeText so Avalonia web can TextBox copy-paste works

src/Web/Avalonia.Web.Blazor/AvaloniaView.razor

@@ -12,7 +12,10 @@
 
 	<div id="nativeControlsContainer" @ref="_nativeControlsContainer" />
 
-    <input id="inputElement" @ref="_inputElement" type="text" oninput="@OnInput"/>
+    <input id="inputElement" @ref="_inputElement" type="text" oninput="@OnInput" 
+        onpaste="return false;"
+        oncopy="return false;" 
+        oncut="return false;"/>
 </div>
 
 <style>

src/Web/Avalonia.Web.Blazor/ClipboardImpl.cs

@@ -0,0 +1,34 @@
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Text;
+using System.Threading.Tasks;
+using Avalonia.Input;
+using Avalonia.Input.Platform;
+using Microsoft.JSInterop;
+
+namespace Avalonia.Web.Blazor
+{
+    internal class ClipboardImpl : IClipboard
+    {
+        public async Task<string> GetTextAsync()
+        {
+            return await AvaloniaLocator.Current.GetRequiredService<IJSInProcessRuntime>().
+                InvokeAsync<string>("navigator.clipboard.readText");
+        }
+
+        public async Task SetTextAsync(string text)
+        {
+            await AvaloniaLocator.Current.GetRequiredService<IJSInProcessRuntime>().
+                InvokeAsync<string>("navigator.clipboard.writeText",text);
+        }
+
+        public Task ClearAsync() => Task.CompletedTask;
+
+        public Task SetDataObjectAsync(IDataObject data) => Task.CompletedTask;
+
+        public Task<string[]> GetFormatsAsync() => Task.FromResult(Array.Empty<string>());
+
+        public Task<object> GetDataAsync(string format) => Task.FromResult<object>(new());
+    }
+}

src/Web/Avalonia.Web.Blazor/WinStubs.cs

@@ -8,21 +8,6 @@ using Avalonia.Platform;
 
 namespace Avalonia.Web.Blazor
 {
-    internal class ClipboardStub : IClipboard
-    {
-        public Task<string> GetTextAsync() => Task.FromResult("");
-
-        public Task SetTextAsync(string text) => Task.CompletedTask;
-
-        public Task ClearAsync() => Task.CompletedTask;
-
-        public Task SetDataObjectAsync(IDataObject data) => Task.CompletedTask;
-
-        public Task<string[]> GetFormatsAsync() => Task.FromResult(Array.Empty<string>());
-
-        public Task<object> GetDataAsync(string format) => Task.FromResult<object>(new ());
-    }
-
     internal class IconLoaderStub : IPlatformIconLoader
     {
         private class IconStub : IWindowIconImpl

src/Web/Avalonia.Web.Blazor/WindowingPlatform.cs

@@ -34,7 +34,7 @@ namespace Avalonia.Web.Blazor
             var instance = new BlazorWindowingPlatform();
             s_keyboard = new KeyboardDevice();
             AvaloniaLocator.CurrentMutable
-                .Bind<IClipboard>().ToSingleton<ClipboardStub>()
+                .Bind<IClipboard>().ToSingleton<ClipboardImpl>()
                 .Bind<ICursorFactory>().ToSingleton<CssCursorFactory>()
                 .Bind<IKeyboardDevice>().ToConstant(s_keyboard)
                 .Bind<IPlatformSettings>().ToConstant(instance)