Auto merge of #50017 - tinaun:stabilize-all-the-things, r=sfackler

stabilize a bunch of minor api additions

besides `ptr::NonNull::cast` (which is 4 days away from end of FCP) all of these have been finished with FCP for a few weeks now with minimal issues raised

* Closes #41020
* Closes #42818
* Closes #44030
* Closes #44400
* Closes #46507
* Closes #47653
* Closes #46344

the following functions will be stabilized in 1.27:
* `[T]::rsplit`
* `[T]::rsplit_mut`
* `[T]::swap_with_slice`
* `ptr::swap_nonoverlapping`
* `NonNull::cast`
* `Duration::from_micros`
* `Duration::from_nanos`
* `Duration::subsec_millis`
* `Duration::subsec_micros`
* `HashMap::remove_entry`

src/libstd/collections/hash/map.rs

@@ -1379,7 +1379,6 @@ impl<K, V, S> HashMap<K, V, S>
     /// # Examples
     ///
     /// ```
-    /// #![feature(hash_map_remove_entry)]
     /// use std::collections::HashMap;
     ///
     /// # fn main() {
@@ -1389,7 +1388,7 @@ impl<K, V, S> HashMap<K, V, S>
     /// assert_eq!(map.remove(&1), None);
     /// # }
     /// ```
-    #[unstable(feature = "hash_map_remove_entry", issue = "46344")]
+    #[stable(feature = "hash_map_remove_entry", since = "1.27.0")]
     pub fn remove_entry<Q: ?Sized>(&mut self, k: &Q) -> Option<(K, V)>
         where K: Borrow<Q>,
               Q: Hash + Eq

src/libstd/lib.rs

@@ -275,7 +275,6 @@
 #![feature(macro_reexport)]
 #![feature(macro_vis_matcher)]
 #![feature(needs_panic_runtime)]
-#![feature(nonnull_cast)]
 #![feature(exhaustive_patterns)]
 #![feature(nonzero)]
 #![feature(num_bits_bytes)]