[js] Dce removes static field with function call

[RblSb]

class Main {
    static final numbers = [];
    static function addNum(n:Int):Int {
        numbers.push(n);
        return n;
    }
    static final node = addNum(1);

    static function main() {
        trace(numbers.length); // 0
    }
}

Fine on eval.

[Simn]

Hmm, I vaguely remember that this is by design, but looking at it now makes me question if that design is any good...

[back2dos]

As mentioned in #10766, I think ideally purity would be taken into account here.