Allow notebook to be closed by pressing Esc

[acelaya]

Part of #6158

#6187 changed the notebook to be displayed in a native dialog when possible.

That PR disabled the default behavior to close the dialog via Esc key, as it didn't work out of the box.

This PR enables that behavior back, and implements the missing logic to make everything work as expected.

Testing steps

1. Open the notebook.
2. Close it via "Close" button.
3. Open it again. Press Esc and verify the notebook is closed and the sidebar is opened.
4. Check that it is possible to open the notebook again, as many times as required.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (1d898d4) 99.44% compared to head (eab7dfd) 99.44%.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #6189      +/-   ##
==========================================
- Coverage   99.44%   99.44%   -0.01%     
==========================================
  Files         266      266              
  Lines       10147    10146       -1     
  Branches     2403     2403              
==========================================
- Hits        10091    10090       -1     
  Misses         56       56              

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[robertknight]

LGTM. As discussed in this thread I do wonder if we can avoid hiding the sidebar when the notebook is open, now that we are using the browser's native modal dialog. We'd have to confirm why we hid the sidebar in the first place when the notebook is opened.