In the `FileList` struct, rename the `AssetLibraryReference
*asset_library` field to `asset_library_ref` -- it's a description of
which asset library is used, and not the asset library itself.
This is to make space for a future `AssetLibrary *asset_library` field,
which will point to an actual asset library struct/class.
No functional changes.
Reviewed by: Severin
Differential Revision: https://developer.blender.org/D12151
9cff9f9f5d