Deprecate the unstable Vec::resize_default

Author: scottmcm

src/liballoc/vec.rs

@@ -1368,6 +1368,7 @@ impl<T: Default> Vec<T> {
     /// # Examples
     ///
     /// ```
+    /// # #![allow(deprecated)]
     /// #![feature(vec_resize_default)]
     ///
     /// let mut vec = vec![1, 2, 3];
@@ -1384,6 +1385,9 @@ impl<T: Default> Vec<T> {
     /// [`Default`]: ../../std/default/trait.Default.html
     /// [`Clone`]: ../../std/clone/trait.Clone.html
     #[unstable(feature = "vec_resize_default", issue = "41758")]
+    #[rustc_deprecated(reason = "This is moving towards being removed in favor \
+        of `.resize_with(Default::default)`.  If you disagree, please comment \
+        in the tracking issue.", since = "1.33.0")]
     pub fn resize_default(&mut self, new_len: usize) {
         let len = self.len();