WIP: fix duplicate get store value

[tanhauhau]

Fix #3375

[Conduitry]

Did you see the couple of failing tests related to SSR?

[tanhauhau]

yea... i havent figured out why...

[ghost]

Hmm, seems the $foo = get_store_value$(foo) is in the wrong spot for SSR code.
It seems like we need to first check if there are store references on the RHS of assignment statements in instance_javascript.

So, we need the main.js code to look like:

	let $foo;
	let foo = writable(42);
-	let { initial_foo = $foo } = $$props;
+	let { initial_foo = $foo = get_store_value$(foo)} = $$props;
	if ($$props.initial_foo === void 0 && $$bindings.initial_foo && initial_foo !== void 0) $$bindings.initial_foo(initial_foo);
-	$foo = get_store_value$(foo);
	return `<p>${escape$(initial_foo)}</p>`;

However, I'm not sure how this will behave with the alternate generator for the main block which loops until settled.

[Conduitry]

Closing in favor of #5419.