fix(rxSortableColumn): use proper ID to pass function to scope

# NOTE This is a *breaking* change. Every instance of `rxSortableColumn` we have will have to be updated.


Everything was technically working properly without this change. I thought functions passed to the scope *had* to be identified with `&`, but maybe not? If someone can show that it's ok to pass a function with `=`, then we can delete this PR and forget this ever happened