feat: Implement of EventTarget

[nabetti1720]

Issue # (if available)

Closes #262

Description of changes

This PR is intended to address the following issues:

• Refactoring of events.rs
• Implementation of globalThis.EventTarget
• Implementation of globalThis.CustomEvent

It is not yet complete in the following respects: 1. type property of CustomEvent is not available. We know that we need to modify EventKey::from_value(). ==>We were able to avoid this by preparing a dedicated dispatchEvent(). 2. the test code is not written yet.

// event_target3.js
const catFound = new CustomEvent("animalfound", {
  detail: {
    name: "cat",
  },
});
const dogFound = new CustomEvent("animalfound", {
  detail: {
    name: "dog",
  },
});

console.log(catFound);
console.log(dogFound);

const obj = new EventTarget()
obj.addEventListener("animalfound", (e) => console.log(e.detail.name));

obj.dispatchEvent(catFound);
obj.dispatchEvent(dogFound);

% ./llrt event_target3.js
CustomEvent {
  detail: {
    name: 'cat'
  },
  type: 'animalfound'
}
CustomEvent {
  detail: {
    name: 'dog'
  },
  type: 'animalfound'
}
cat
dog

Checklist

• [x] Created unit tests in tests/unit and/or in Rust for my feature if needed
• [x] Ran make fix to format JS and apply Clippy auto fixes
• [x] Made sure my code didn't add any additional warnings: make check
• [x] Updated documentation if needed (API.md/README.md/Other)

By submitting this pull request, I confirm that you can use, modify, copy, and redistribute this contribution, under the terms of your choice.

[nabetti1720]

I think it is fine as a minimal implementation. Please merge if you have no problem with the review.