Rollup merge of rust-lang#113657 - Urgau:expand-incorrect_fn_null_check-lint, r=cjgillot

Expand, rename and improve `incorrect_fn_null_checks` lint

This PR,

 - firstly, expand the lint by now linting on references
 - secondly, it renames the lint `incorrect_fn_null_checks` -> `useless_ptr_null_checks`
 - and thirdly it improves the lint by catching `ptr::from_mut`, `ptr::from_ref`, as well as `<*mut _>::cast` and `<*const _>::cast_mut`

Fixes rust-lang#113601
cc ```@est31```

Author: matthiaskrgr

core/src/ptr/mod.rs

@@ -710,6 +710,7 @@ pub const fn from_ref<T: ?Sized>(r: &T) -> *const T {
 #[inline(always)]
 #[must_use]
 #[unstable(feature = "ptr_from_ref", issue = "106116")]
+#[rustc_diagnostic_item = "ptr_from_mut"]
 pub const fn from_mut<T: ?Sized>(r: &mut T) -> *mut T {
     r
 }

core/src/ptr/mut_ptr.rs

@@ -54,6 +54,7 @@ impl<T: ?Sized> *mut T {
     /// Casts to a pointer of another type.
     #[stable(feature = "ptr_cast", since = "1.38.0")]
     #[rustc_const_stable(feature = "const_ptr_cast", since = "1.38.0")]
+    #[rustc_diagnostic_item = "ptr_cast"]
     #[inline(always)]
     pub const fn cast<U>(self) -> *mut U {
         self as _