feat: emit change event when toggle task in viewer

[jajugoguma]

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Description

• Added feature to emit a "change" event when a task's checkbox is toggled in the viewer.
  • This was added as there is no way to notify that the content in the viewer has changed due to a checkbox toggle.

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[adhrinae]

LGTM.
그런데 실제 토글 시 이벤트가 수신되는지 체크하는 테스트는 작성하는게 어려운가봐요?

[jajugoguma]

@adhrinae
이벤트 발생 자체를 확인것은 어렵지는 않은데, 체크박스가 별도의 요소가 아닌 슈도 요소이고, mousedown을 체크박스 요소가 있는 위치에 발생시키는 것을 실패했습니다... 이를 테스트하려면 테스트가 실제 브라우저 상에서 동작해야할 것 같습니다...

[jwlee1108]

리뷰 완료합니다.

[TheoBiron]

Shouldn't this update the value of the markdown editor too ?
Right now, the markdown is not edited, and the data sent through the event emitted doesnt help to re-build the markdown content

[jwlee1108]

@TheoBiron

That's a good question. we'll check it. but, the viewer is a light and simple module that uses only toastMark. I don't think there will be a big problem, but we'll do additional work considering the side effects.