Trigger GhostCells On Cell Execution (#1744)

* Fix

* Cleanup.

* Update the comment.

* Try to use onDidChangeActiveTextEditors and onDidChangeVisibleTextEditors; that doesn't work. probably because the outputs aren't text editors.

* Start hacking on using the notebook change event.

* Success we appear to be successfully trigger when output updates and output appears to get sent at least if the cell is non-interactive.

* Add comment.

* Comment out changes to try to see why execution in non-interactive cells is no longer working.

* Revert "Comment out changes to try to see why execution in non-interactive cells is no longer working."

This reverts commit 2d650a6.

* Cleanup.

* Revert changes to trigger completions on doExecute. It seems redundant.

* Revert examples

* Revert changes to contributing.md

* Add lock file

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Co-authored-by: Sebastian Tiedtke <sebastiantiedtke@gmail.com>