Rollup merge of #89899 - jkugelman:must-use-alloc, r=joshtriplett
Add #[must_use] to remaining alloc functions
I've run out of compelling reasons to group functions together across crates so I'm just going to go module-by-module. This is everything remaining from the `alloc` crate.
I ignored these because they might be used to purposefully leak memory... or other allocator shenanigans? I dunno. I'll add them if y'all tell me to.
```rust
alloc::alloc unsafe fn alloc(layout: Layout) -> *mut u8;
alloc::alloc unsafe fn alloc_zeroed(layout: Layout) -> *mut u8;
alloc::sync::Arc<T> fn into_raw(this: Self) -> *const T;
```
I don't know why clippy ignored these. I added them myself:
```rust
alloc::collections::btree_map::BTreeMap<K, V> fn range<T: ?Sized, R>(&self, range: R) -> Range<'_, K, V>;
alloc::collections::btree_set::BTreeSet<T> fn range<K: ?Sized, R>(&self, range: R) -> Range<'_, T>;
```
I added these non-mutating `mut` functions:
```rust
alloc::collections::btree_map::BTreeMap<K, V> fn range_mut<T: ?Sized, R>(&mut self, range: R) -> RangeMut<'_, K, V>;
alloc::collections::btree_map::BTreeMap<K, V> fn iter_mut(&mut self) -> IterMut<'_, K, V>;
alloc::collections::btree_map::BTreeMap<K, V> fn values_mut(&mut self) -> ValuesMut<'_, K, V>;
alloc::collections::linked_list::LinkedList<T> fn iter_mut(&mut self) -> IterMut<'_, T>;
alloc::collections::linked_list::LinkedList<T> fn cursor_front_mut(&mut self) -> CursorMut<'_, T>;
alloc::collections::linked_list::LinkedList<T> fn cursor_back_mut(&mut self) -> CursorMut<'_, T>;
alloc::collections::linked_list::LinkedList<T> fn front_mut(&mut self) -> Option<&mut T>;
alloc::collections::linked_list::LinkedList<T> fn back_mut(&mut self) -> Option<&mut T>;
alloc::collections::linked_list::CursorMut<'a, T> fn current(&mut self) -> Option<&mut T>;
alloc::collections::linked_list::CursorMut<'a, T> fn peek_next(&mut self) -> Option<&mut T>;
alloc::collections::linked_list::CursorMut<'a, T> fn peek_prev(&mut self) -> Option<&mut T>;
alloc::collections::linked_list::CursorMut<'a, T> fn front_mut(&mut self) -> Option<&mut T>;
alloc::collections::linked_list::CursorMut<'a, T> fn back_mut(&mut self) -> Option<&mut T>;
```
I moved a few existing `#[must_use]`s from functions onto the iterator types they return: `IntoIterSorted`, `IntoKeys`, `IntoValues`.
Parent issue: #89692
r? `@joshtriplett`
1adb664392