Don't run ImplicitlyExpandNETStandardFacades if disabled

Previously I added a safeguard to ensure ImplicitlyExpandNETStandardFacades would run
before the OOB conflict resolution, but I didn't condition that on the property which
disables ImplicitlyExpandNETStandardFacades.  The result is that if someone was using
this in a non-SDK project and tried to disable ImplicitlyExpandNETStandardFacades it wouldn't
be disabled.

Author: ericstj

pkg/NETStandard.Library.NETFramework/targets/NETStandard.Library.NETFramework.common.targets

@@ -24,7 +24,7 @@
     </Otherwise>
   </Choose>
 
-  <PropertyGroup>
+  <PropertyGroup Condition="'$(ImplicitlyExpandNETStandardFacades)' == 'true'">
     <!-- Ensure this runs before conflict resolution since the added files may cause conflicts -->
     <HandlePackageFileConflictsDependsOn>ImplicitlyExpandNETStandardFacades;$(HandlePackageFileConflictsDependsOn)</HandlePackageFileConflictsDependsOn>
   </PropertyGroup>