Rollup merge of #49858 - dmizuk:unique-doc-hidden, r=steveklabnik

std: Mark `ptr::Unique` with `#[doc(hidden)]`

`Unique` is now perma-unstable, so let's hide its docs.

src/liballoc/boxed.rs

@@ -184,6 +184,7 @@ impl<T: ?Sized> Box<T> {
 
     #[unstable(feature = "ptr_internals", issue = "0", reason = "use into_raw_non_null instead")]
     #[inline]
+    #[doc(hidden)]
     pub fn into_unique(b: Box<T>) -> Unique<T> {
         let unique = b.0;
         mem::forget(b);

src/libcore/ptr.rs

@@ -2513,6 +2513,7 @@ impl<T: ?Sized> PartialOrd for *mut T {
            reason = "use NonNull instead and consider PhantomData<T> \
                      (if you also use #[may_dangle]), Send, and/or Sync")]
 #[allow(deprecated)]
+#[doc(hidden)]
 pub struct Unique<T: ?Sized> {
     pointer: NonZero<*const T>,
     // NOTE: this marker has no consequences for variance, but is necessary