Blender Git Loki

LibOverride: add recursive resync.

Recursive resync means also resyncing overrides that are linked from
other library files into current working file.

Note that this allows to get 'working' files even when their
dependencies are out of sync. However, since linked data is never
written/saved, this has to be re-done every time the working file is
loaded, until said dependencies are updated properly.

NOTE: This is still missing the 'report' side of things, which is part
of a larger task to enhance reports regarding both linking, and
liboverrides (see T88393).

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Technical notes:

Implementing this proved to be slightly more challenging than expected,
mainly because one of the key aspects of the feature was never done in
Blender before: manipulating, re-creating linked data.

This ended up moving the whole resync code to use temp IDs out of bmain,
which is better in the long run anyway (and more aligned with what we
generally want to do when manipulating temp ID data). It should also
give a marginal improvement in performances for regular resync.

This commit also had to carefully 'sort' libraries by level of indirect
usage, as we want to resync first the libraries that are the least directly
used, i.e. libraries that are most used by other libraries.