Rollup merge of #101727 - est31:stabilize_map_first_last, r=m-ou-se

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](rust-lang/rust#62924 (comment)) finishing.~~ Edit: It finished!

Author: matthiaskrgr