stabilize the poll_map feature

Author: KodrAus

library/core/src/task/poll.rs

@@ -84,7 +84,7 @@ impl<T, E> Poll<Result<T, E>> {
 
 impl<T, E> Poll<Option<Result<T, E>>> {
     /// Changes the success value of this `Poll` with the closure provided.
-    #[unstable(feature = "poll_map", issue = "63514")]
+    #[stable(feature = "poll_map", since = "1.51.0")]
     pub fn map_ok<U, F>(self, f: F) -> Poll<Option<Result<U, E>>>
     where
         F: FnOnce(T) -> U,
@@ -98,7 +98,7 @@ impl<T, E> Poll<Option<Result<T, E>>> {
     }
 
     /// Changes the error value of this `Poll` with the closure provided.
-    #[unstable(feature = "poll_map", issue = "63514")]
+    #[stable(feature = "poll_map", since = "1.51.0")]
     pub fn map_err<U, F>(self, f: F) -> Poll<Option<Result<T, U>>>
     where
         F: FnOnce(E) -> U,