Make ptr_cast_add_auto_to_object lint into hard error

In Rust 1.81, we added a FCW lint (including linting in dependencies)
against pointer casts that add an auto trait to dyn bounds.  This was
part of work making casts of pointers involving trait objects stricter
which was needed to restabilize trait upcasting.

We considered just making this a hard error at the time, but opted
against it due to breakage found by crater.  This breakage was mostly
due to the `anymap` crate which has been a persistent problem for us.

It's now a year later, and the fact that this is not yet a hard error
is giving us pause about stabilizing arbitrary self types and
`derive(CoercePointee)`.  So let's now make a hard error of this.

compiler/rustc_lint/src/lib.rs

@@ -601,6 +601,11 @@ fn register_builtins(store: &mut LintStore) {
         "converted into hard error, \
          see <https://github.com/rust-lang/rust/issues/73333> for more information",
     );
+    store.register_removed(
+        "ptr_cast_add_auto_to_object",
+        "converted into hard error, see issue #127323 \
+         <https://github.com/rust-lang/rust/issues/127323> for more information",
+    );
 }
 
 fn register_internals(store: &mut LintStore) {