Stabilize map_first_last Stabilizes the following functions: ```Rust impl<T> BTreeSet<T> { pub fn first(&self) -> Option<&T> where T: Ord; pub fn last(&self) -> Option<&T> where T: Ord; pub fn pop_first(&mut self) -> Option<T> where T: Ord; pub fn pop_last(&mut self) -> Option<T> where T: Ord; } impl<K, V> BTreeMap<K, V> { pub fn first_key_value(&self) -> Option<(&K, &V)> where K: Ord; pub fn last_key_value(&self) -> Option<(&K, &V)> where K: Ord; pub fn first_entry(&mut self) -> Option<OccupiedEntry<'_, K, V>> where K: Ord; pub fn last_entry(&mut self) -> Option<OccupiedEntry<'_, K, V>> where K: Ord; pub fn pop_first(&mut self) -> Option<(K, V)> where K: Ord; pub fn pop_last(&mut self) -> Option<(K, V)> where K: Ord; } ``` Closes #62924 ~~Blocked on the [FCP](https://github.com/rust-lang/rust/issues/62924#issuecomment-1179489929) finishing.~~ Edit: It finished!