docs: Fix outdated doc comments about allocating 'at least' the requested size

The 'at least' behavior of the Allocator interface was removed in #13666, so anything that used reallocAtLeast or the .at_least Exact behavior could still have doc comments that reference no-longer-true behavior.

Funnily enough, ArrayList is the only place that used this functionality (outside of allocator test cases), so its doc comments are the only things that need to be fixed. This was checked by resetting to deda6b5 and searching for all instances of `reallocAtLeast` and `.at_least` (one of which would need to be used to get the `.at_least` behavior)

Author: squeek502

lib/std/array_list.zig

@@ -60,8 +60,8 @@ pub fn ArrayListAligned(comptime T: type, comptime alignment: ?u29) type {
             };
         }
 
-        /// Initialize with capacity to hold at least `num` elements.
-        /// The resulting capacity is likely to be equal to `num`.
+        /// Initialize with capacity to hold `num` elements.
+        /// The resulting capacity will equal `num` exactly.
         /// Deinitialize with `deinit` or use `toOwnedSlice`.
         pub fn initCapacity(allocator: Allocator, num: usize) Allocator.Error!Self {
             var self = Self.init(allocator);
@@ -379,9 +379,9 @@ pub fn ArrayListAligned(comptime T: type, comptime alignment: ?u29) type {
             return self.ensureTotalCapacityPrecise(better_capacity);
         }
 
-        /// Modify the array so that it can hold at least `new_capacity` items.
-        /// Like `ensureTotalCapacity`, but the resulting capacity is much more likely
-        /// (but not guaranteed) to be equal to `new_capacity`.
+        /// Modify the array so that it can hold `new_capacity` items.
+        /// Like `ensureTotalCapacity`, but the resulting capacity is guaranteed
+        /// to be equal to `new_capacity`.
         /// Invalidates pointers if additional memory is needed.
         pub fn ensureTotalCapacityPrecise(self: *Self, new_capacity: usize) Allocator.Error!void {
             if (@sizeOf(T) == 0) {
@@ -570,8 +570,8 @@ pub fn ArrayListAlignedUnmanaged(comptime T: type, comptime alignment: ?u29) typ
             return if (alignment) |a| ([:s]align(a) T) else [:s]T;
         }
 
-        /// Initialize with capacity to hold at least num elements.
-        /// The resulting capacity is likely to be equal to `num`.
+        /// Initialize with capacity to hold `num` elements.
+        /// The resulting capacity will equal `num` exactly.
         /// Deinitialize with `deinit` or use `toOwnedSlice`.
         pub fn initCapacity(allocator: Allocator, num: usize) Allocator.Error!Self {
             var self = Self{};
@@ -885,9 +885,9 @@ pub fn ArrayListAlignedUnmanaged(comptime T: type, comptime alignment: ?u29) typ
             return self.ensureTotalCapacityPrecise(allocator, better_capacity);
         }
 
-        /// Modify the array so that it can hold at least `new_capacity` items.
-        /// Like `ensureTotalCapacity`, but the resulting capacity is much more likely
-        /// (but not guaranteed) to be equal to `new_capacity`.
+        /// Modify the array so that it can hold `new_capacity` items.
+        /// Like `ensureTotalCapacity`, but the resulting capacity is guaranteed
+        /// to be equal to `new_capacity`.
         /// Invalidates pointers if additional memory is needed.
         pub fn ensureTotalCapacityPrecise(self: *Self, allocator: Allocator, new_capacity: usize) Allocator.Error!void {
             if (@sizeOf(T) == 0) {