Add 'EnableXamlCompilerMismatchedTfmUnoWorkaround'

Author: Sergio0694

MultiTarget/Extra.props

@@ -14,7 +14,7 @@
 
   <!-- Workaround, improved error message when consuming from Uno projects with mismatched TFMs -->
   <!-- See https://github.com/CommunityToolkit/Windows/issues/388 -->
-  <ItemGroup>
+  <ItemGroup Condition="'$(EnableXamlCompilerMismatchedTfmUnoWorkaround)' == 'true'">
     <None PackagePath="lib/net9.0-windows10.0.18362" Include="$(MSBuildThisFileDirectory)/_._" Pack="true" />
     <None PackagePath="lib/net8.0-windows10.0.18362" Include="$(MSBuildThisFileDirectory)/_._" Pack="true" />
     <None PackagePath="lib/net7.0-windows10.0.18362" Include="$(MSBuildThisFileDirectory)/_._" Pack="true" />

MultiTarget/MultiTargetIdentifiers.props

@@ -49,6 +49,11 @@
 
     <IsUno Condition="'$(IsWasm)' == 'true' OR '$(IsWpf)' == 'true' OR '$(IsGtk)' == 'true' OR '$(IsDroid)' == 'true' OR '$(IsMacOS)' == 'true' OR '$(IsiOS)' == 'true'">true</IsUno>
 
+    <!--
+      Provide an opt-out switch for https://github.com/CommunityToolkit/Tooling-Windows-Submodule/issues/185.
+      This causes problems for UWP packages just targeting 17763 or other lower TFMs, as it conflicts with this.
+    -->
+    <EnableXamlCompilerMismatchedTfmUnoWorkaround Condition="'$(EnableXamlCompilerMismatchedTfmUnoWorkaround)' == ''">true</EnableXamlCompilerMismatchedTfmUnoWorkaround>
 
     <!--
       This property is only for changing the version used by Uno.