This now works by getting the RNA Path from the given PointerRNA to go from the
ID block to the data it points to, then uses this path to find the new data
relative to the COW ID.
Note: This currently still has all the debug prints left in - As can be seen,
I was testing this against the earlier PoseBone hack/special case. We may still
need to bring such special cases back in future, since looking up RNA Paths
like this can be slow.
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