Blender Git Loki

LibOverride: Improve speed of resync and creation of liboverrides.

`BKE_collection_object_find` has extremely bad performances (very high
time complexity). While ideally this should be fixed in that API, for
now cache its results once at the beginning of the resync/creation
process.

This makes loading of complex production files with a lot of
liboverrides to resync three to four times faster.

Thanks to @brecht for the profiling in T94059.