Add net8.0-windows10.0.22621.0 and required flags to Uwp TFMs

Author: Arlodotexe

MultiTarget/AvailableTargetFrameworks.props

@@ -1,6 +1,6 @@
 <Project>
     <PropertyGroup>
-        <UwpTargetFramework>uap10.0.17763</UwpTargetFramework>
+        <UwpTargetFramework>uap10.0.17763;net8.0-windows10.0.22621.0;</UwpTargetFramework>
         <WinAppSdkTargetFramework>net8.0-windows10.0.22621.0;net7.0-windows10.0.22621.0;net6.0-windows10.0.22621.0;</WinAppSdkTargetFramework>
 
         <WasmHeadTargetFramework>net8.0</WasmHeadTargetFramework>

MultiTarget/EnabledTargetFrameworks.props

@@ -1,6 +1,6 @@
 <Project>
     <PropertyGroup>
-        <UwpTargetFramework>uap10.0.17763</UwpTargetFramework>
+        <UwpTargetFramework>uap10.0.17763;net8.0-windows10.0.22621.0;</UwpTargetFramework>
         <WinAppSdkTargetFramework>net8.0-windows10.0.22621.0;net7.0-windows10.0.22621.0;net6.0-windows10.0.22621.0;</WinAppSdkTargetFramework>
 
         <WasmHeadTargetFramework>net8.0</WasmHeadTargetFramework>

MultiTarget/MultiTargetIdentifiers.props

@@ -59,5 +59,8 @@
      -->
     <WinUIMajorVersion Condition="'$(HasWinUI)' == 'true' AND '$(IsUwp)' == 'true'">2</WinUIMajorVersion>
     <WinUIMajorVersion Condition="'$(HasWinUI)' == 'true' AND '$(IsWinAppSdk)' == 'true'">3</WinUIMajorVersion>
+
+    <UseUwp Condition="'$(HasWinUI)' == 'true' AND '$(IsUwp)' == 'true'">true</UseUwp>
+    <UseUwpTools Condition="'$(HasWinUI)' == 'true' AND '$(IsUwp)' == 'true'">true</UseUwpTools>
   </PropertyGroup>
 </Project>

ProjectHeads/App.Head.Uwp.props

@@ -2,7 +2,7 @@
   <Import Project="$(MSBuildExtensionsPath)\$(MSBuildToolsVersion)\Microsoft.Common.props" Condition="Exists('$(MSBuildExtensionsPath)\$(MSBuildToolsVersion)\Microsoft.Common.props')" />
 
   <PropertyGroup>
-    <TargetFramework>$(UwpTargetFramework)</TargetFramework>
+    <TargetFramework>$(UwpTargetFramework.Split(';')[0])</TargetFramework>
     <DependencyVariant>Uwp</DependencyVariant>
   </PropertyGroup>