Vec: IntoIterator signature consistency

Also makes the code dryer.

Author: ripytide

library/alloc/src/vec/mod.rs

@@ -2780,7 +2780,7 @@ impl<T, A: Allocator> IntoIterator for Vec<T, A> {
     /// assert_eq!(v_iter.next(), None);
     /// ```
     #[inline]
-    fn into_iter(self) -> IntoIter<T, A> {
+    fn into_iter(self) -> Self::IntoIter {
         unsafe {
             let mut me = ManuallyDrop::new(self);
             let alloc = ManuallyDrop::new(ptr::read(me.allocator()));
@@ -2808,7 +2808,7 @@ impl<'a, T, A: Allocator> IntoIterator for &'a Vec<T, A> {
     type Item = &'a T;
     type IntoIter = slice::Iter<'a, T>;
 
-    fn into_iter(self) -> slice::Iter<'a, T> {
+    fn into_iter(self) -> Self::IntoIter {
         self.iter()
     }
 }
@@ -2818,7 +2818,7 @@ impl<'a, T, A: Allocator> IntoIterator for &'a mut Vec<T, A> {
     type Item = &'a mut T;
     type IntoIter = slice::IterMut<'a, T>;
 
-    fn into_iter(self) -> slice::IterMut<'a, T> {
+    fn into_iter(self) -> Self::IntoIter {
         self.iter_mut()
     }
 }