misc: add AcceptableKeys demo.

demo/Ursa.Demo/Pages/KeyGestureInputDemo.axaml

@@ -5,11 +5,16 @@
     xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
     xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
     xmlns:u="https://irihi.tech/ursa"
+    xmlns:vm="clr-namespace:Ursa.Demo.ViewModels;assembly=Ursa.Demo"
     d:DesignHeight="450"
     d:DesignWidth="800"
+    x:CompileBindings="True"
+    x:DataType="vm:KeyGestureInputDemoViewModel"
     mc:Ignorable="d">
     <StackPanel Margin="20">
+        <TextBlock Text="Accept all keys" />
         <u:KeyGestureInput HorizontalAlignment="Left" />
-        <u:KeyGestureInput HorizontalAlignment="Left" />
+        <TextBlock Text="Accept only A,B and C" />
+        <u:KeyGestureInput HorizontalAlignment="Left" AcceptableKeys="{Binding AcceptableKeys}" />
     </StackPanel>
 </UserControl>

demo/Ursa.Demo/ViewModels/KeyGestureInputDemoViewModel.cs

@@ -1,8 +1,13 @@
+using System.Collections.Generic;
+using Avalonia.Input;
 using CommunityToolkit.Mvvm.ComponentModel;
 
 namespace Ursa.Demo.ViewModels;
 
 public class KeyGestureInputDemoViewModel: ObservableObject
 {
-    
+    public List<Key> AcceptableKeys { get; set; } = new List<Key>()
+    {
+        Key.A, Key.B, Key.C,
+    };
 }