export {foo as default} results in a live binding

[Rich-Harris]

See demo:

// main.js
import foo from './foo.js';
console.log( foo ); // expected 1, got 2

// foo.js
let foo = 1;
export { foo as default }; // `export default foo` works correctly
foo = 2;

This should log 1 but logs 2. Via #845

[guybedford]

@Rich-Harris I don't think this is correct actually. It is only export default asdf that is not live as that is an expression form, but export { x as default } should be live like any other binding.