Rollup merge of rust-lang#103489 - WaffleLapkin:byte_offset_from_you,…

… r=scottmcm

Make `pointer::byte_offset_from` more generic

As suggested by rust-lang#96283 (comment) (cc `@scottmcm),` make `pointer::byte_offset_from` work on pointers of different types. `byte_offset_from` really doesn't care about pointer types, so this is totally fine and, for example, allows patterns like this:
```rust
ptr::addr_of!(x.b).byte_offset_from(ptr::addr_of!(x))
```

The only possible downside is that this removes the `T` == `U` hint to inference, but I don't think this matter much. I don't think there are a lot of cases where you'd want to use `byte_offset_from` with a pointer of unbounded type (and in such cases you can just specify the type).

`@rustbot` label +T-libs-api

library/core/src/ptr/const_ptr.rs

@@ -709,7 +709,7 @@ impl<T: ?Sized> *const T {
     #[unstable(feature = "pointer_byte_offsets", issue = "96283")]
     #[rustc_const_unstable(feature = "const_pointer_byte_offsets", issue = "96283")]
     #[cfg_attr(miri, track_caller)] // even without panics, this helps for Miri backtraces
-    pub const unsafe fn byte_offset_from(self, origin: *const T) -> isize {
+    pub const unsafe fn byte_offset_from<U: ?Sized>(self, origin: *const U) -> isize {
         // SAFETY: the caller must uphold the safety contract for `offset_from`.
         unsafe { self.cast::<u8>().offset_from(origin.cast::<u8>()) }
     }

library/core/src/ptr/mut_ptr.rs

@@ -889,7 +889,7 @@ impl<T: ?Sized> *mut T {
     #[unstable(feature = "pointer_byte_offsets", issue = "96283")]
     #[rustc_const_unstable(feature = "const_pointer_byte_offsets", issue = "96283")]
     #[cfg_attr(miri, track_caller)] // even without panics, this helps for Miri backtraces
-    pub const unsafe fn byte_offset_from(self, origin: *const T) -> isize {
+    pub const unsafe fn byte_offset_from<U: ?Sized>(self, origin: *const U) -> isize {
         // SAFETY: the caller must uphold the safety contract for `offset_from`.
         unsafe { self.cast::<u8>().offset_from(origin.cast::<u8>()) }
     }