clippy::identity-op triggering on 1 << 0

[cramertj]

When writing bitflags it's convenient to structure code like this:

const X: usize = 1 << 0;
const Y: usize = 1 << 1;
const Z: usize = 1 << 2;

Clippy lints against the 1 << 0 because it has no effect. This is a fairly common structure-- it'd be nice to perhaps make an exception for this specific case.

[hcpl]

Duplicate of #3430?

[cramertj]

Yup! I searched but didn't see it. Thanks!