Fix conditional PackageReference being ignored VS by moving into dedicated files.

Author: Arlodotexe

MultiTarget/PackageReferences/Uwp.props

@@ -1,9 +1,4 @@
 <Project>
-  <ItemGroup>
-    <PackageReference Condition="'$(HasWinUI)' == 'true'" Include="Microsoft.UI.Xaml" Version="2.8.7-prerelease.241119001" />
-    <PackageReference Condition="'$(MultiTargetPlatformIdentifier)' == 'windows'" Include="Microsoft.Windows.CsWinRT" Version="2.1.6" PrivateAssets="all" />
-
-    <!-- Temp workaround until next Windows SDK servicing update -->
-    <PackageReference Condition="'$(HasWinUI)' == 'true' AND '$(MultiTargetPlatformIdentifier)' == 'windows' AND '$(IsDeployableHead)' != 'true'" Include="Microsoft.Windows.SDK.CPP" Version="10.0.26100.2454" PrivateAssets="all" />
-  </ItemGroup>
+	<!-- The inner imports in these props are conditional, and must be in a <When> statement in their own file to work in Visual Studio. https://stackoverflow.com/a/16557059 -->
+	<Import Project="$(MSBuildThisFileDirectory)/Uwp/*.props" />
 </Project>

MultiTarget/PackageReferences/Uwp/Microsoft.UI.Xaml.props

@@ -0,0 +1,13 @@
+<Project>
+	<!-- Condition must be on a <When> statement in its own file for this to work in Visual Studio. https://stackoverflow.com/a/16557059 -->
+	<Choose>
+    <!-- Temp workaround until next Windows SDK servicing update -->
+		<When Condition="'$(HasWinUI)' == 'true'" >
+			<ItemGroup>
+				<PackageReference Include="Microsoft.UI.Xaml" Version="2.8.7-prerelease.241119001" />
+			</ItemGroup>
+		</When>
+		<Otherwise>
+		</Otherwise>
+	</Choose>
+</Project>

MultiTarget/PackageReferences/Uwp/Microsoft.Windows.CsWinRT.props

@@ -0,0 +1,13 @@
+<Project>
+	<!-- Condition must be on a <When> statement in its own file for this to work in Visual Studio. https://stackoverflow.com/a/16557059 -->
+	<Choose>
+    <!-- Temp workaround until next Windows SDK servicing update -->
+		<When Condition="'$(MultiTargetPlatformIdentifier)' == 'windows'" >
+			<ItemGroup>
+				<PackageReference Include="Microsoft.Windows.CsWinRT" Version="2.1.6" PrivateAssets="all" />
+			</ItemGroup>
+		</When>
+		<Otherwise>
+		</Otherwise>
+	</Choose>
+</Project>

MultiTarget/PackageReferences/Uwp/Microsoft.Windows.SDK.CPP.props

@@ -0,0 +1,13 @@
+<Project>
+	<!-- Condition must be on a <When> statement in its own file for this to work in Visual Studio. https://stackoverflow.com/a/16557059 -->
+	<Choose>
+    <!-- Temp workaround until next Windows SDK servicing update -->
+		<When Condition="'$(HasWinUI)' == 'true'" >
+			<ItemGroup>
+				<PackageReference Include="Microsoft.Windows.SDK.CPP" Version="10.0.26100.2454" PrivateAssets="all" />
+			</ItemGroup>
+		</When>
+		<Otherwise>
+		</Otherwise>
+	</Choose>
+</Project>