This commit mainly addresses issues when a part of an override hierarchy
does not match anymore the linked reference data, and gets isolated form
the hierarchy root (there is no parenting chain to the root anymore).
The typical case being an object or sub-collection being moved to
another subcollection in the linked data.
Case identified while working on some Pets production files.
Note that in some cases this isolated chunk of the hierarchy will be
linked back into the appropriate place, in others it should be fully
removed (instead of staying as unused data). The later will be handled
in a another future commit.
This commit mainly detect and use a new tag for such cases, and correct
the checks to take it into account.
It also does a bit of cleanup, and replaces some asserts by `CLOG_ERROR`
reports.
5574a1bfc1