8$: error on multiple 'export default'-s

[strager]

export default class A {}
export default class B {}

The above code is invalid. quick-lint-js should report something like the following:

line 2: error: cannot export default more than once
line 1: note: export default previously appeared here

[k1ng440]

I want to give this a try. I can't promise a good clean code though because this is going to be my first time contributing to C++ codebase and I will not accept payment.