Stop moving to next cell when suggestion widget is visible

[jonah-iden]

What it does

This disables the moving to another notebook cell via the arrow keys when the suggestion widget is open

How to test

1. Open a notebook with at least two cells.
2. Pressing arrow down when on the last line of should then focus the next cell
3. Type something in the cell to reveal suggestions
4. Pressing the up arrow now should not move back to the first cell but only the selection inside the suggestion widget

Follow-ups

Review checklist

• As an author, I have thoroughly tested my changes and carefully followed the review guidelines

Reminder for reviewers

• As a reviewer, I agree to behave in accordance with the review guidelines

[msujew]

LGTM 👍