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 https://github.com/rust-lang/rust/issues/113601
cc ```@est31```
7518ae566e