fix(ext/web): Copy EventTarget list before dispatch (#19360)

Related issue: https://github.com/denoland/deno/issues/19358.

This is a regression that seems to have been introduced in
https://github.com/denoland/deno/pull/18905. It looks to have been a
performance optimization.

The issue is probably easiest described with some code:
```ts
const target = new EventTarget();
const event = new Event("foo");
target.addEventListener("foo", () => {
  console.log('base');
  target.addEventListener("foo", () => {
    console.log('nested');
  });
});
target.dispatchEvent(event);
```
Essentially, the second event listener is being attached while the `foo`
event is still being dispatched. It should then not fire that second
event listener, but Deno currently does.

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