Mark declaration, not just identifier, as unused

[jrieken]

re #50487

• have the snippet below
• not how just the a is marked as unused but not the whole declaration

class TestMe {

    constructor(b: boolean);
    constructor(b: string)
    constructor(b: boolean | string, a?: boolean) {
        console.log(b);
    }

    callMe(): any {
        interface Foo {
            bar: boolean;
        }

        let bazz: Foo;

        return bazz;
    }
}

[jrieken]

Related to this: if a class/interface isn't used its member aren't used, right?

[mjbvz]

Opened microsoft/TypeScript#24598 and microsoft/TypeScript#24597 for some of these

We decided not to mark the entire class/function bodies as unused because users often start writing them and only reference them later. Greying out the entire thing could get in the way