Autosubscribed stores no longer listed as referenced in vars

[Conduitry]

Describe the bug
Since #3945, autosubscribing to a store within the template no longer causes the store to be marked as referenced: true in the vars response from the compiler.

Logs
n/a

To Reproduce

<script>
	let store;
</script>
{$store}

Compile this, and look at the vars value in the response. store has referenced: false.

Expected behavior
store should have referenced: true.

Stacktraces
n/a

Information about your Svelte project:
Svelte 3.16.0, 3.16.1

Severity
Moderate. Causing new incorrect warnings in the ESLint plugin - sveltejs/eslint-plugin-svelte3#49

Additional context
Unlike the above, this seems to be working correctly:

<script>
	let store;
	$store;
</script>

[ghost]

Another interesting thing is that $store has referenced: true in the first case but not the second. Looking at the debugger, the first case only calls add_reference on the $store variable name.

There's code in that method here to check for an auto-subscribe so we should probably just also tag it with referenced = true.

PR on the way... just running CI tests now.

[ghost]

Bah... marking the store as referenced creates a codegen test failure....

[ghost]

Actually, I think the change to the expected output is OK since it used to be there before @Rich-Harris made his changes (though in a different order).

[anlexN]

@Conduitry why do you have to use this syntax?

[Conduitry]

What syntax? I'm not sure what you're asking.

[anlexN]

let store;
$store;