Consolidated GlobalUsings and introduced EnableGlobalUsings property. Respects HasWinUI.

Author: Arlodotexe

MultiTarget/GlobalUsings.props

@@ -0,0 +1,6 @@
+<Project>
+  <ItemGroup>
+    <Compile Condition="'$(EnableGlobalUsings)' != 'false' AND '$(HasWinUI)' == 'true'" Include="$(ToolingDirectory)\GlobalUsings_WinUI.cs" />
+    <Compile Condition="'$(EnableGlobalUsings)' != 'false'" Include="$(ToolingDirectory)\GlobalUsings.cs" />
+  </ItemGroup>
+</Project>

MultiTarget/Library.props

@@ -17,6 +17,7 @@
   <Import Project="$(ToolingDirectory)\MultiTarget\MultiTargetIdentifiers.props" />
   <Import Project="$(ToolingDirectory)\MultiTarget\DefinedConstants.props" />
   <Import Project="$(ToolingDirectory)\MultiTarget\NoWarn.props"/>
+  <Import Project="$(ToolingDirectory)\MultiTarget\GlobalUsings.props" />
 
   <!-- Add platform package dependencies -->
   <Import Project="$(ToolingDirectory)\MultiTarget\PackageReferences\Uno.props" Condition="$(IsUno) == 'true'" />

MultiTarget/WinUI.Extra.props

@@ -62,10 +62,6 @@
     <NoWarn>$(NoWarn);CA1416;</NoWarn>
   </PropertyGroup>
 
-  <ItemGroup>
-    <Compile Include="$(ToolingDirectory)\GlobalUsings_WinUI.cs" />
-  </ItemGroup>
-
   <!-- Workaround for Mac: https://developercommunity.visualstudio.com/t/XamarinMac-binaries-are-missing-in-173/10164443#T-N10164676 10/6/22 -->
   <ItemGroup Condition=" $(TargetFramework.StartsWith('xamarinmac')) ">
     <Reference Include="Xamarin.Mac">