Move MefConstruction helper to shared code

src/Workspaces/SharedUtilitiesAndExtensions/Workspace/Core/WorkspaceExtensions.projitems

@@ -76,6 +76,7 @@
     <Compile Include="$(MSBuildThisFileDirectory)Workspace\Mef\IMefHostExportProvider.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)Workspace\Mef\LanguageMetadata.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)Workspace\Mef\LanguageServiceMetadata.cs" />
+    <Compile Include="$(MSBuildThisFileDirectory)Workspace\Mef\MefConstruction.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)Workspace\Mef\MefLanguageServices.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)Workspace\Mef\MefWorkspaceServices.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)Workspace\Mef\OrderableLanguageMetadata.cs" />