Implement lint against dangerous implicit autorefs

Author: Urgau

alloc/src/vec/mod.rs

@@ -2588,7 +2588,7 @@ impl<T, A: Allocator> Vec<T, A> {
     #[inline]
     #[track_caller]
     unsafe fn append_elements(&mut self, other: *const [T]) {
-        let count = unsafe { (*other).len() };
+        let count = other.len();
         self.reserve(count);
         let len = self.len();
         unsafe { ptr::copy_nonoverlapping(other as *const T, self.as_mut_ptr().add(len), count) };