Fix the 'Show All' bone collection operator, by making it operate on all
collections instead of just the roots. It also now ensures that all
ancestors of the solo'ed collection are shown (otherwise it's the only
visible one, but given that its parent is hidden, it's still not
visible).
This also fixes a related issue, where calling the operator without
passing the `name` parameter would do nothing. Now it soloes the active
bone collection.
2274f2be4b