Reference XliffTasks conditionally

Go back to only bringing in the `XliffTasks` package in projects with
shipping binaries. It turns out some non-shipping projects use a
different set of NuGet feeds that do not include `XliffTasks`, causing
the signed build to fail when we try to restore them.

This also requires we update the loc check to go through a target
conditioned on shipping projects, since the
`EnsureAllResourcesTranslated` target will no longer be available in all
projects.

build/Targets/Imports.targets

@@ -38,15 +38,10 @@
   </PropertyGroup>
 
   <ItemGroup>
-    <PackageReference Include="XliffTasks" Version="$(XliffTasksVersion)" PrivateAssets="All" />
+    <PackageReference Include="XliffTasks" Version="$(XliffTasksVersion)" PrivateAssets="All" Condition="'$(NonShipping)' != 'true'" />
     <PackageReference Include="Microsoft.SourceLink.GitHub" Version="$(MicrosoftSourceLinkGitHubVersion)" PrivateAssets="All" />
   </ItemGroup>
 
-  <PropertyGroup>
-    <!-- Disable localization for non-shipping projects -->
-    <EnableXlfLocalization Condition="'$(NonShipping)' == 'true'">false</EnableXlfLocalization>
-  </PropertyGroup>
-
   <Choose>
     <When Condition="'$(SignAssembly)' == 'true'">
       <Choose>
@@ -500,4 +495,13 @@
   </PropertyGroup>
 
   <Import Project="RepoToolset\SymStore.targets" />
+
+  <!--
+    Delegates to XliffTasks to validate that all localizable resources have been translated.
+    We can't use EnsureAllResoucesTranslated directly because the XliffTasks package is only pulled in by projects that
+    produce shipping binaries.
+  -->
+  <Target Name="CheckLocStatus"
+          DependsOnTargets="EnsureAllResourcesTranslated"
+          Condition="'$(NonShipping)' != 'true'" />
 </Project>

build/scripts/build.ps1

@@ -482,7 +482,7 @@ function Build-DeployToSymStore() {
 }
 
 function Build-CheckLocStatus() {
-    Run-MSBuild "Roslyn.sln" "/t:EnsureAllResourcesTranslated" -logFileName "RoslynCheckLocStatus"
+    Run-MSBuild "Roslyn.sln" "/t:CheckLocStatus" -logFileName "RoslynCheckLocStatus"
 }
 
 # These are tests that don't follow our standard restore, build, test pattern. They customize