Closes #25854

You can now drag-and-drop on the remaining space in the project panel to
drop entries/external paths in the last worktree.


https://github.com/user-attachments/assets/a7e14518-6065-4b0f-ba2c-823c70f154f4

Release Notes:

- Added support for drag-and-drop files and external paths into the
empty space of the project panel, placing them in the last folder you
have added to the project.