Dirty flag not removed when undoing changes.

When using VS Code with the Vim extension, I notice that:

In Vim: If you make changes to a file and then undo those changes using the u key, Vim recognizes that the buffer content matches the original file on disk. As a result, it clears the modified flag (+ in the filename) and doesn't prompt you to save upon exit.

In VS Code with Vim Extension: After making changes and undoing them with u, VS Code still marks the file as modified (indicated by a dot ● in the file tab or a dirty indicator), even though the file content matches the saved version. This means VS Code prompts you to save the file upon closing, even when no actual changes exist.

Vim's behaviour is really helpful when having changed a file accidentally, as it shows when being back to the original state by removing the dirty flag.

No source file or test is named. First reproduce the issue in VS Code with the Vim extension by editing a file and undoing with the u key, then trace the extension's undo and dirty-state handling. Done means returning to the saved content clears the dirty indicator and avoids an unnecessary save prompt.