Components allow const/class/function exports to be overridden

[Rich-Harris]

REPL. This code...

<script>
	export let a = 1;
	export const b = 2;
</script>

...results in this:

let { a = 1 } = $$props;
const { b = 2 } = $$props;

That's wrong — it should be this instead:

let { a = 1 } = $$props;
const b = 2;