add a lint [unused_any_all]: the return values of Iterator::{any,all} are not used.

[RGafiyatullin]

---

Adding a lint that checks for not using the return values from Iterator::any or Iterator::all.

changelog: added a new lint — [unused_any_all]

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[nyurik]

isn't this what #[must_use] is for?

[RGafiyatullin]

@nyurik true.

For some reason I thought it would only work when put over a type, not over a method.
I should probably go and try proposing having this attribute over these methods of the Iterator trait.

Sorry for distracting you :)