Lint on pointer comparisons for non-thin pointers.

[scottmcm]

Per the 2023-11-08 lang triage meeting, lang would like to see a lint like the one in the second bullet from #106447 (comment) :

Deprecate comparisons (Eq/Ord) on dyn trait pointers by adding a lint which encourages people to case the pointer to *mut u8 first. This makes the intent of such comparisons much clearer.

The lint should not warn on comparison of thin pointers.

When non-thin pointers are compared (whether with == or != or PartialEq methods directly), the lint should warn, suggesting that you do one of the following instead:

• call https://doc.rust-lang.org/nightly/std/ptr/fn.eq.html if you really wanted to compare both the address and the metadata
• call https://doc.rust-lang.org/nightly/std/ptr/fn.addr_eq.html (or just .cast::<()>()) if you only want to compare the addresses