Stabilize vec_spare_capacity

Closes rust-lang#75017

Author: Amanieu

Diff for: library/alloc/src/vec/mod.rs

@@ -2043,8 +2043,6 @@ impl<T, A: Allocator> Vec<T, A> {
     /// # Examples
     ///
     /// ```
-    /// #![feature(vec_spare_capacity)]
-    ///
     /// // Allocate vector big enough for 10 elements.
     /// let mut v = Vec::with_capacity(10);
     ///
@@ -2061,7 +2059,7 @@ impl<T, A: Allocator> Vec<T, A> {
     ///
     /// assert_eq!(&v, &[0, 1, 2]);
     /// ```
-    #[unstable(feature = "vec_spare_capacity", issue = "75017")]
+    #[stable(feature = "vec_spare_capacity", since = "1.60.0")]
     #[inline]
     pub fn spare_capacity_mut(&mut self) -> &mut [MaybeUninit<T>] {
         // Note:

Diff for: library/alloc/tests/lib.rs

@@ -31,7 +31,6 @@
 #![feature(iter_advance_by)]
 #![feature(slice_group_by)]
 #![feature(slice_partition_dedup)]
-#![feature(vec_spare_capacity)]
 #![feature(string_remove_matches)]
 #![feature(const_btree_new)]
 #![feature(const_default_impls)]

Diff for: library/core/src/mem/maybe_uninit.rs

@@ -1038,7 +1038,7 @@ impl<T> MaybeUninit<T> {
     /// ```
     ///
     /// ```
-    /// #![feature(maybe_uninit_write_slice, vec_spare_capacity)]
+    /// #![feature(maybe_uninit_write_slice)]
     /// use std::mem::MaybeUninit;
     ///
     /// let mut vec = Vec::with_capacity(32);
@@ -1098,7 +1098,7 @@ impl<T> MaybeUninit<T> {
     /// ```
     ///
     /// ```
-    /// #![feature(maybe_uninit_write_slice, vec_spare_capacity)]
+    /// #![feature(maybe_uninit_write_slice)]
     /// use std::mem::MaybeUninit;
     ///
     /// let mut vec = Vec::with_capacity(32);

Diff for: library/std/src/lib.rs

@@ -341,7 +341,6 @@
 #![feature(unboxed_closures)]
 #![feature(unwrap_infallible)]
 #![feature(vec_into_raw_parts)]
-#![feature(vec_spare_capacity)]
 // NB: the above list is sorted to minimize merge conflicts.
 #![default_lib_allocator]