Uplift clippy::double_neg lint as double_negations

[kadiwa4]

Warns about cases like this:

fn main() {
    let x = 1;
    let _b = --x; //~ WARN use of a double negation
}

The intent is to keep people from thinking that --x is a prefix decrement operator. ++x, x++ and x-- are invalid expressions and already have a helpful diagnostic.

I didn't add a machine-applicable suggestion to the lint because it's not entirely clear what the programmer was trying to achieve with the --x operation. The code that triggers the lint should always be reviewed manually.

Closes #82987

[rustbot]

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[rustbot]

Some changes occurred in src/tools/clippy

cc @rust-lang/clippy

[kadiwa4]

@rustbot author

[nnethercote]

This needs T-lang approval. The appropriate labels have been applied to summon them.

[bors]

☔ The latest upstream changes (presumably #127174) made this pull request unmergeable. Please resolve the merge conflicts.

[kadiwa4]

@rustbot ready

[nnethercote]

Still waiting on T-lang, AFAICT.

[kadiwa4]

@rustbot label: -S-waiting-on-review +S-waiting-on-team

[bors]

☔ The latest upstream changes (presumably #128985) made this pull request unmergeable. Please resolve the merge conflicts.