Svelte 5 rewrite

Kinda closes #11316: although the code in their repro will still not work because you can't spread classes into arguments this allow to create properties with literals like

class Toggle{
    "aria-pressed" = $state(true);
}

that get's compiled to

class Toggle {
    #aria_pressed = $.source(true);

    get "aria-pressed"() {
        return $.get(this.#aria_pressed);
    }

    set "aria-pressed"(value) {
        $.set(this.#aria_pressed, $.proxy(value));
    }
}

i've added a single test for this but i'm wondering if i should add a test for each class test that was already there (in theory it should already be covered because they share the same code but you know)

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