fix: more robust handling of var declarations

[dummdidumm]

• fixes Svelte 5: using var with $state is brittle #12807: state declared with var is now retrieved using a new safe_get function, which works like get but checks for undefined
• fixes Svelte 5: $state declared with var in *.svelte.js broken #12900: ensure we're not creating another new scope for block statements of function declarations, which resulted in var declarations getting "swallowed" (because they were hoisted to the function declaration scope and never seen by our logic)

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Latest commit: 77c528c

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[trueadm]

I actually love the simplicity of this for var vs the amount of work required to handle the oddities the other way.

[dummdidumm]

yeah adding a new hoisting mechanism to the state, which is tied to the nearest scope etc etc felt way to involved for this. Also, it wouldn't stop there, you'd have to hoist and then update the signal in a special way.

console.log(x);
var x = $state(..);
// -->
var x = $.source();
console.log($.get(x));
x.v = ...;

All that additional code for such a niche thing doesn't feel worth the additional overhead, which is why I went with this solution.