Blender Git Loki

LibOverride: Create override operator: various fixes.

* `make_override_library_exec` was not properly cleaning `LIB_TAG_DOIT`
from all IDs in the Main DB.
* `BKE_override_library_create_from_tag` was doing dangerous things
(like iterating over a BMain listbase while adding items to it...).
* It would remap *all* local usages of overridden linked IDs to new
overriding local IDs, which was very inconvinient.

New handling of remapping now allows to only remap inside of the group
of IDs that is being overridden, in other words you can still have e.g.
other empties still instancing the same linked collection...