Fixed an issue where switching to WinUI 3 would break UWP

Author: Arlodotexe

MultiTarget/Library.props

@@ -8,12 +8,12 @@
   <!-- Get the enabled MultiTarget features for this project / run -->
   <Import Project="$(ToolingDirectory)\MultiTarget\EnabledMultiTargets.props" />
   <Import Project="$(ToolingDirectory)\MultiTarget\EnabledTargetFrameworks.props" />
+  <Import Project="$(ToolingDirectory)\MultiTarget\WinUI.TargetVersion.props" />
 
   <!-- Use <MultiTarget> values to define <TargetFrameworks> -->
   <Import Project="$(ToolingDirectory)\MultiTarget\MultiTargetToTargetFramework.props" />
 
   <!-- Enable project identifiers -->
-  <Import Project="$(ToolingDirectory)\MultiTarget\WinUI.TargetVersion.props" />
   <Import Project="$(ToolingDirectory)\MultiTarget\MultiTargetIdentifiers.props" />
   <Import Project="$(ToolingDirectory)\MultiTarget\DefinedConstants.props" />
 

MultiTarget/MultiTargetIdentifiers.props

@@ -51,5 +51,12 @@
     <IsUno Condition="'$(IsWasm)' == 'true' OR '$(IsWpf)' == 'true' OR '$(IsGtk)' == 'true' OR '$(IsDroid)' == 'true' OR '$(IsMacOS)' == 'true' OR '$(IsiOS)' == 'true'">true</IsUno>
 
     <HasWinUI Condition="'$(IsUwp)' == 'true' OR '$(IsWinAppSdk)' == 'true' OR '$(IsUno)' == 'true'">true</HasWinUI>
+
+    <!--
+      This property is only for changing the version used by Uno.
+      Force the version to 2 for UWP and 3 for WinAppSDK.
+     -->
+    <WinUIMajorVersion Condition="'$(IsUwp)' == 'true'">2</WinUIMajorVersion>
+    <WinUIMajorVersion Condition="'$(IsWinAppSdk)' == 'true'">3</WinUIMajorVersion>
   </PropertyGroup>
 </Project>

ProjectHeads/SingleComponent/Wasm/ProjectTemplate.Wasm.csproj

@@ -5,6 +5,7 @@
     <IsUno>true</IsUno>
     <IsWasm>true</IsWasm>
     <IsWasmHead>true</IsWasmHead>
+    <HasWinUI>true</HasWinUI>
 
     <IsSingleExperimentHead>true</IsSingleExperimentHead>
   </PropertyGroup>