Set WindowIcon in csproj to apply it to all surfaces. Updated icon to include all scales.

Fixed #4575.

code/TemplateStudioForWinUICs/TemplateStudioForWinUICs.csproj

@@ -243,9 +243,6 @@
     <Content Include="Templates\Ft\AppNotifications\Param_ProjectName\Services\AppNotificationService.cs">
       <IncludeInVSIX>true</IncludeInVSIX>
     </Content>
-    <Content Include="Templates\Proj\Default\Param_ProjectName\Usings.cs">
-      <IncludeInVSIX>true</IncludeInVSIX>
-    </Content>
     <Content Include="Templates\Proj\Default\Param_ProjectName\Helpers\TitleBarHelper.cs">
       <IncludeInVSIX>true</IncludeInVSIX>
     </Content>
@@ -2322,4 +2319,4 @@
   <Target Name="AfterBuild">
   </Target>
   -->
-</Project>
+</Project>

code/TemplateStudioForWinUICs/Templates/Proj/Default/Param_ProjectName/MainWindow.xaml.cs

@@ -8,7 +8,6 @@ public sealed partial class MainWindow : WindowEx
     {
         InitializeComponent();
 
-        AppWindow.SetIcon(Path.Combine(AppContext.BaseDirectory, "Assets/WindowIcon.ico"));
         Content = null;
         Title = "AppDisplayName".GetLocalized();
     }

code/TemplateStudioForWinUICs/Templates/Proj/Default/Param_ProjectName/Param_ProjectName.csproj

@@ -5,6 +5,7 @@
     <TargetPlatformMinVersion>10.0.17763.0</TargetPlatformMinVersion>
     <RootNamespace>Param_RootNamespace</RootNamespace>
     <ApplicationManifest>app.manifest</ApplicationManifest>
+    <ApplicationIcon>Assets/WindowIcon.ico</ApplicationIcon>
     <Platforms>x86;x64;arm64</Platforms>
     <RuntimeIdentifiers>win10-x86;win10-x64;win10-arm64</RuntimeIdentifiers>
     <PublishProfile>Properties\PublishProfiles\win10-$(Platform).pubxml</PublishProfile>