When creating etc. a liboverride based on a partial hierarchy
pre-selection (e.g: override hierarchy on the rig object of a
character), now all linked data also using that rig (e.g. all meshes
deformed by that armature) will also automatically be overridden.
This si achieved by following dependencies in the reversed order (from
used IDs to using IDs) when we find one tagged for override.
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