Fix shadow_unrelated's behaviour with closures

[DJMcNab]

Fixes #10780

We correctly no longer give a warning when a closure is passed to a method, where one of the arguments to that method uses the variable which would be shadowed by an argument to that closure.
Uses is defined loosely as any expression used in the calling expression mentions the shadowee binding (except for the closure itself):

#![deny(clippy::shadow_unrelated)]
let x = Some(1);
let y = x.map(|x| x + 1);

will now succeed.

See linebender/xilem#745 - without this change, all of the expect(shadow_unrelated) in the repository are met; with it, none of them are.

changelog: [shadow_unrelated]: Don't treat closures arguments as unrelated when the calling function uses them

[rustbot]

r? @Jarcho

rustbot has assigned @Jarcho.
They will have a look at your PR within the next two weeks and either review your PR or reassign to another reviewer.

Use r? to explicitly pick a reviewer

[Jarcho]

Thank you.