breaking: change $state.frozen -> $state.raw

[Rich-Harris]

closes #12434. This replaces $state.frozen with $state.raw, which no longer adds STATE_FROZEN_SYMBOL or uses Object.freeze — it leaves its argument untouched, and just creates a source for it.

Draft because one test, around each block updates, is currently failing. This is because each blocks use STATE_FROZEN_SYMBOL to determine what kind of optimisations to apply.

I'd like to explore whether there are alternative ways to think about this. I'm not a huge fan of the runtime checking anyway — it only works in simple cases (each numbers, but not each numbers.filter(is_even), etc). I think it's possible that we could get further with the compiler (though there might be some tricky caveats about props crossing runes/non-runes boundaries and so on) — for example we could definitely improve cases like this:

{#each [1, 2, 3] as n}
  <p>{n}</p>
{/each}

-$.each(node, 1, () => [1, 2, 3], $.index, ($$anchor, n, $$index) => {
+$.each(node, 1, () => [1, 2, 3], $.index, ($$anchor, n) => {
  var p = root_1();
  var text = $.child(p);

  $.reset(p);
-  $.template_effect(() => $.set_text(text, $.unwrap(n)));
+  $.set_text(text, n);
  $.append($$anchor, p);
});

Will likely investigate these ideas in other PRs and circle back to this one.

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[Rich-Harris]

merge conflicts are out of control — closing in favour of #12742