557b3d2762
Adds `mark_asset()` and `clear_asset()` to ID data-blocks, e.g. `bpy.context.active_object.mark_asset()`. They essentially do the same as the mark and clear asset operators. Scripts are generally discouraged from using operators where possible, but we need to provide API functions to use instead. In this case it means scripts don't have to override context to pass an ID to the operator.