The operator stored when registering the asset shelf will be called
with properties that reference the asset (a weak reference, split into
three properties already used in other asset-related operators). The
operator is called whenever a grid view item is activated, and is
meant to do things like import and activate a brush asset.
Previously Reviewed: https://projects.blender.org/blender/blender/pulls/117861
Pull Request: https://projects.blender.org/blender/blender/pulls/121402
798219225d