enhance: use EventName on window's once and remove listener before calling handler

[Legend-Master]

• Use EventName on Window, Webview and WebviewWindow's once
• Unlisten before calling handler on once so we always unlisten the event even if the callback throws, also allow that unlisten's error to not get caught
• Also refactored some other things

[Legend-Master]

Note that I don't think once on Window works with tauri://created and tauri://error, the handler is not removed after it gets called, I'm not familiar with how window specific event works, so I didn't fix that part