Blender Git Loki

Fix T70875: Library Override: Clicking an Library Overriden Object crashes Blender.

We also need to rebuild the whole collection/viewlayer object cache
thing when we relink an objector collection in a collection (since it
might be part of a view layer).

Again, usual disclaimer about how inneficient this is currently, needs a
serious refactor to only tag caches as dirty, and actually rebuild the
whole thing on access.