Find all references for ambient module

// declarations.d.ts
declare module "x" {
    export const x: number;
}

// index.ts
import {x} from "x";

Goto-declaration for "x" in index.ts works, but find-all-references for "x" in declarations.d.ts finds only itself.

In this case one can simply look through each of export in the module's body and find all of their references; but for shorthand ambient modules (declare module "x";) that won't work, as there is no module body.

Reproduce the behavior using the declarations.d.ts and index.ts snippets, then trace the find-all-references path for the ambient module and its exported symbol. Done means references from index.ts are included when searching from declarations.d.ts, with shorthand ambient modules also handled; add or update coverage for both forms.