Run CollectPackageReferences on dynamically referenced projects for N…

…uGet.

This gets the project.assets.json to contain all of the right things so
that the Runner project gets transitive dependencies from dynamically referenced
projects (in this case, Injectable).

Runner/Build/AddDynamicReferences.targets

@@ -40,4 +40,21 @@
       <ProjectReference Include="@(MyDynamicProjectReference)"/>
     </ItemGroup>
   </Target>
+  <!--
+      Make up for NuGet’s inability to collect package references by
+      loading them from dependencies. This way, we can make transitive
+      dependencies sort of work.
+  -->
+  <Target BeforeTargets="CollectPackageReferences" DependsOnTargets="MyCollectDynamicProjectReferences" Name="MyCollectPackageReferences">
+    <MSBuild
+        BuildInParallel="$(BuildInParallel)"
+        Projects="@(MyDynamicProjectReference)"
+        Targets="CollectPackageReferences"
+        >
+      <Output
+          ItemName="PackageReference"
+          TaskParameter="TargetOutputs"
+          />
+    </MSBuild>
+  </Target>
 </Project>