Preload System.Text.Json 8.0.0.4

This works around dotnet/sdk#43339 by preloading a copy of the assembly
that can't be located with the normal load processes. It should be
harmless (other than wasting time) in circumstances where it's not
necessary.

Directory.Build.targets

@@ -37,4 +37,30 @@
     <RemoveDir Directories="$(_PackageFolderInGlobalPackages)"
                Condition="Exists('$(_PackageFolderInGlobalPackages)')" />
   </Target>
+
+  <!-- BEGIN workaround for https://github.com/dotnet/sdk/issues/43339; remove after updated to VS 17.12 or a future 17.11 patch -->
+  <Target Name="WorkaroundDotnetSdk43339" BeforeTargets="ResolvePackageAssets" Condition=" '$(MSBuildRuntimeType)' == 'Full' and $([MSBuild]::VersionLessThan($(MSBuildVersion), 17.12.0))">
+    <PrimeSystemTextJson804 />
+  </Target>
+  <UsingTask
+    TaskName="PrimeSystemTextJson804"
+    TaskFactory="RoslynCodeTaskFactory"
+    AssemblyFile="$(MSBuildToolsPath)\Microsoft.Build.Tasks.Core.dll" >
+    <Task>
+      <Code Type="Fragment" Language="cs">
+<![CDATA[
+try
+{
+    System.Reflection.Assembly.LoadFrom(@"$(MicrosoftNETBuildTasksDirectoryRoot)\..\..\..\DotnetTools\dotnet-format\BuildHost-net472\System.Text.Json.dll");
+}
+catch
+{
+    // Best effort: if something moves in the SDK don't break the build.
+}
+]]>
+      </Code>
+    </Task>
+  </UsingTask>
+  <!-- END workaround for https://github.com/dotnet/sdk/issues/43339 -->
+
 </Project>