fix: make $state component exports settable

[dummdidumm]

fixes #11983

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Latest commit: 71cd00a

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[FoHoOV]

This works as the tests say, but if we just try to use the "assign directly" method by removing the increment function it doesnt work. It seems if we never try to mutate the state within that component, then it just changes into a normal variable.

with increment:

export default function Counter($$anchor, $$props) {
	$.push($$props, true);

	let count = $.source(0);
        // other stuff
	return $.pop({
		get count() {
			return $.get(count);
		},
		set count($$value) {
			$.set(count, $.proxy($$value));
		},
		get doubled() {
			return $.get(doubled);
		},
		increment
	});

without increment:

export default function Counter($$anchor, $$props) {
	$.push($$props, true);

	let count = 0;
        // other stuff
	return $.pop({
		get count() {
			return count;
		},
		set count($$value) {
			count = $$value;
		},
		get doubled() {
			return $.get(doubled);
		}
	});

Edit: this behavior is not related to this PR, but seems to break what people or at least I would expect it to do.

Edit2: because of this maybe?

export function is_state_source(binding, state) {
	return (
		(binding.kind === 'state' || binding.kind === 'frozen_state') &&
		(!state.analysis.immutable || binding.reassigned || state.analysis.accessors)
	);
}

[Rich-Harris]

good spot — fixed