Fixes that type/feature mappings are not available during setup

[gvkries]

This reverts some of the changes made by #15793. Especially, the population of the ITypeFeatureProvider was completley moved into the ShellContainerFactory. But this is too late e.g. for the CompositionStrategy which already requires some types being populated.

So I've moved that part back to the ExtensionManager, where it originally was done before #15793. This does not change the new behavior of having multiple features per type or the automatic detection of the feature without the FeatureAttribute, but the split responsibility of adding types to the ITypeFeatureProvider is now back.

Fixes #16289

[Piedone]

This looks OK to me, but I'm out of my depth here so would defer to others.

This indeed fixed the symptoms of #16289. What exactly in the changes fixes that BTW? What got stuck in App_Data after not running the setup?