Stabilize const `BTree{Map,Set}::new` The FCP was completed in #71835. Since `len` and `is_empty` are not const stable yet, this also creates a new feature for them since they previously used the same `const_btree_new` feature.
Stabilize const `BTree{Map,Set}::new` The FCP was completed in #71835. Since `len` and `is_empty` are not const stable yet, this also creates a new feature for them since they previously used the same `const_btree_new` feature.