Autosave support

[dwelle]

When you open/load a file using the new FS, we should support opt-in autosaving during the editing session.

Upon close, if changes aren't saved, it should nevertheless prompt to save changes (#2728) regardless of the opt-in status.

[artemanufrij]

Hey guys, I lost a lot of my work because I opened a new file for just check something. Please implement a opt-in auto save function!

[sojusnik]

Lost some of my work again, because my local file wasn't autosaved :(

Is the implementation of autosave still on the table?

[yangls06]

I have the same requirement. Losing the drawing is annoying.

[ken-okabe]

To those concerned with this issue, I recommend you to use:
Excalidraw for Visual Studio Code
https://github.com/excalidraw/excalidraw-vscode
https://marketplace.visualstudio.com/items?itemName=pomdtr.excalidraw-editor

It's easier to manage local files by VSCode's native file management and, of course, auto-saving feature included.

[loganvolkers]

This was started in PR #3047 but that was years ago and it might need updating.