fixes for invisible cells

[jonah-iden]

What it does

Fixes deleting cell outputs or cells with outputs while there are invisible cells.

How to test

Best way to test is probably adding something like

        return this.cells.filter(cell => !(cell.metadata.custom as { metadata: { hidden: boolean } })?.metadata?.hidden);

to the getVisibleCells method of the NotebookModel. Then opening the notebook with the text editor and add "hidden":true to the metadata.

Then open the notebook normally and test moving and deleting cells and outputs.

Follow-ups

Breaking changes

• This PR introduces breaking changes and requires careful review. If yes, the breaking changes section in the changelog has been updated.

Attribution

Review checklist

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

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