Rename and allow `cast_ref_to_mut` lint

This PR is a small subset of rust-lang/rust#112431, that is the renaming of the lint (`cast_ref_to_mut` -> `invalid_reference_casting`).

BUT also temporarily change the default level of the lint from deny-by-default to allow-by-default until rust-lang/rust#112431 is merged.

r? `@Nilstrieb`