This one was a bit more involved than the previous ones, since the
mismatch was intentional here, and happened on a non-trivial type.
It was done because the new object (managed by the `unique_ptr`) steals
the internal data of the original object. Calling `MEM_delete` (and
therefore the destructor of the `AssetMetaData` object) would then lead
to access-after-free and double-freeing errors.
This is addressed by adding two new 'copy' and 'move' constructors to this type.
The copy one ensures that deep-copy of internal data happens as expected, and
allows to simplify greatly the code in `BKE_asset_metadata_copy`, which
becomes a mere wrapper around it.
The move one allows `make_unique` to properly steal (and clear) the internal
data of the source object, which can then safely be deleted.
Pull Request: https://projects.blender.org/blender/blender/pulls/123693
da05bff96c