Show an error when trying to rename a notebook to an existing file

[jtpio]

Description

Attempting to rename a notebook by clicking on the name of the notebook and entering a name that already exists results in an error in the Dev Tools console.

Uncaught (in promise) ResponseError: File already exists: Untitled.ipynb

Reproduce

notebook-rename-existing-file.mp4

Expected behavior

If a notebook with the same name already exists on disk, it should show an error message to the user instead of logging it in the Dev Tools console.

Context

Jupyter Notebook 7.5.0a2 on main: 0e4fdd1

To implement the fix, we likely need to update the handling of the error here:

notebook/packages/application-extension/src/index.ts

Line 661 in 0e4fdd1

const result = await renameDialog(docManager, current.context);