Rollup merge of rust-lang#136877 - Sky9x:const-inherent-ptr-replace, r=jhpratt

Fix missing const for inherent pointer `replace` methods

`ptr::replace` (the free fn) is already const stable. However, there are inherent convenience methods on `*mut T` and `NonNull<T>`, allowing you to write eg. `unsafe { foo.replace(bar) }` where `foo` is `*mut T` or `NonNull<T>`.

It seems const was never added to the inherent method (likely oversight), so this PR adds it.
I don't believe this needs another[^1] FCP as the inherent methods are already stable and `ptr::replace` is already const stable, so this adds no new API.

Original tracking issue: rust-lang#83164
`ptr::replace` constified in rust-lang#83091
`ptr::replace` const stabilized in rust-lang#130954

[^1]: `const_replace` FCP completed: rust-lang#83164 (comment)

Author: matthiaskrgr

core/src/ptr/mut_ptr.rs

@@ -1574,8 +1574,9 @@ impl<T: ?Sized> *mut T {
     ///
     /// [`ptr::replace`]: crate::ptr::replace()
     #[stable(feature = "pointer_methods", since = "1.26.0")]
+    #[rustc_const_stable(feature = "const_inherent_ptr_replace", since = "CURRENT_RUSTC_VERSION")]
     #[inline(always)]
-    pub unsafe fn replace(self, src: T) -> T
+    pub const unsafe fn replace(self, src: T) -> T
     where
         T: Sized,
     {

core/src/ptr/non_null.rs

@@ -1166,7 +1166,8 @@ impl<T: ?Sized> NonNull<T> {
     /// [`ptr::replace`]: crate::ptr::replace()
     #[inline(always)]
     #[stable(feature = "non_null_convenience", since = "1.80.0")]
-    pub unsafe fn replace(self, src: T) -> T
+    #[rustc_const_stable(feature = "const_inherent_ptr_replace", since = "CURRENT_RUSTC_VERSION")]
+    pub const unsafe fn replace(self, src: T) -> T
     where
         T: Sized,
     {