Lint against `--foo` when `foo` is a numeric binding

[estebank]

As noted in #88553 (comment), let x = --y; is syntactically valid as a double negation, but it looks like C's pre-decrement. We should lint against it and suggest both removing the -- or writing y -= 1; let x = y;.

pre-increment, post-increment and post-decrement are not likely to confuse people too much because they are syntax errors, but we might also want to modify the parser to detect them specifically and provide a structured suggestion for appropriate code.

[camelid]

Isn't there a clippy lint that's proposed to be uplifted that catches --y? See #82987.

[estebank]

Yeah, you're right. We can still keep this ticket open for the "handle ++x/x++/x-- more gracefully in the parser".

[camelid]

We can still keep this ticket open for the "handle ++x/x++/x-- more gracefully in the parser".

I think #83502 might cover that. I've been meaning to get back to it...