ResavePackages commandlet with -fixupredirects flag won't update asset references on shared collections

We currently have two methods of fixing up redirectors: the ResavePackages commandlet and the Fix Up option within the editor. While the editor's option correctly handles collections via FAssetFixUpRedirectors::SaveReferencingCollections, there's no equivalent functionality in UResavePackagesCommandlet. As a result, fixed-up assets will be missing from collections, and opening the collection asset in a text editor will show that the old path is still there.

1. Create a new project and connect to source control
2. Create a new asset, and check it in
3. Create a shared collection, which will be automatically checked in. Add your asset.
4. Close the editor. Run the Resave Packages commandlet. I used: 

   UE4Editor.exe <Project Location> -run=ResavePackages -fixupredirects -skipfails -autocheckoutpackages -ignorechangelist -projectonly -crashforuat -stdout

1. Submit your project to source control. You should see the redirector being deleted, and any referencing assets being modified to point to the new location
2. Open the project and view your collection. The fixed-up asset will be missing.