Fix CommonJS rewrites in shorthand destructuring defaults

[Copilot]

Imported and exported identifiers used inside shorthand destructuring default initializers were emitted unchanged in CommonJS output, causing runtime ReferenceErrors.

• Identifier reference detection

  • Treat ShorthandPropertyAssignment.ObjectAssignmentInitializer as an expression reference position.
  • This allows existing CommonJS substitution logic to rewrite imported/exported identifiers there.

• Regression coverage

  • Added a compiler emit test covering both imported and exported identifiers in shorthand destructuring defaults.

import { imported } from "./b";
export const exported = 2;
let a, b;
({ a = imported, b = exported } = {});

now emits:

({ a = b_1.imported, b = exports.exported } = {});