Make question_mark to remove redundant block when outer scope will not be polluted

[profetia]

Closes #16892

Implemented reusing the logic from match_single_binding.

changelog: [question_mark] remove redundant block when outer scope will not be polluted

[rustbot]

r? @Jarcho

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[profetia]

r? clippy

[dswij]

can we also add the case where there is a shadowing inside the block?

e.g.

    if let Some(x) = Some(1) {
        let x = x + 1;
        todo!()
    } else {
        return None;
    };

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[rustbot]

☔ The latest upstream changes (possibly #17607) made this pull request unmergeable. Please resolve the merge conflicts.