Add loading indicator to OpenWith on MacOS and hide it after fully loaded

src/PicView.Avalonia.MacOS/Views/OpenWithView.axaml

@@ -13,6 +13,7 @@
     xmlns:customControls="clr-namespace:PicView.Avalonia.CustomControls;assembly=PicView.Avalonia"
     xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
     xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
+    xmlns:uc="clr-namespace:PicView.Avalonia.Views.UC;assembly=PicView.Avalonia"
     xmlns:viewModels="clr-namespace:PicView.Avalonia.ViewModels;assembly=PicView.Avalonia"
     xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml">
     <Design.DataContext>
@@ -22,6 +23,7 @@
         Background="#4D000000"
         Height="400"
         Width="300">
+        <uc:SpinWaiter x:Name="SpinWaiter" />
         <TextBlock
             Classes="txt"
             FontFamily="avares://PicView.Avalonia/Assets/Fonts/Roboto-Medium.ttf#Roboto"

src/PicView.Avalonia.MacOS/Views/OpenWithView.axaml.cs

@@ -91,6 +91,7 @@ public partial class OpenWithView : Window
 
                     ParentPanel.Children.Add(btn);
                 }
+                SpinWaiter.IsVisible = false;
             });
         });
     }