[arithmetic_side_effects] Constant fields are ignored

[c410-f3r]

struct Foo {
  bar: u32,
}
const FOO: Foo = Foo { bar: 2 };
let _ = 10 / FOO.bar;

In fact, this is an issue that involves anything that uses clippy_utils::consts::constant.

[c410-f3r]

@rustbot claim