This commit is a preparation for an actual change in behavior of
automatic liboverride hierarchies creation. Although it may introduce
some minor changes (fixes) in behavior in some corner-cases, it is
not expected to have any noticeable end-user changes.
The main change is some refactor of the `LibOverrideGroupTagData` util
struct, to make it more clear and easy to manage data (IDs) from linked
reference, and data from liboverrides.
In addition, some minor changes in code logic, either optimizations or
hardened checks, e.g. to skip any processing of hierarchies when the
linked reference of its root is missing, or to ensure that libraries are
matching, etc.
Bastien Montagne
1e50987d94