Add partialeq_to_none lint
Initial implementation of #9275, adding lint `partialeq_to_none`. This is my first time working on `clippy`, so please review carefully.
I'm unsure especially about the `Sugg`, as it covers the entire `BinOp`, instead of just covering one of the sides and the operator (see the multi-line example). I was unsure if pinpointing the suggestion wouldn't be brittle...
changelog: [`PARTIALEQ_TO_NONE`]: Initial commit