Execution of Notebooks are very slow compared to Classic Jupyter

[DonJayamanne]

Run 200 cells in classic Jupyter = 0.5s
Run 200 cells in custom Editor = 9s
Run 200 cells in Native Editor = 35s

Last year I recall making some changes to ensure the perf was faster

Suggestions:

• Synchronize messages only when we have widgets (I did this last year, either the code has been accidentally removed or still there & not workign, or other)
• Don't wait for VS Code to update the output

[DonJayamanne]

We're back at 9-10s in Native notebooks, back to what it was with Custom Editor Notebooks.

Not sure we'll be able to get to 0.5s, as we run each cell sequentially instead of sending all cells to Jupyter Kernel (i.e. we run a cell, check if it fails, then proceed to the next cell).
Considering this only decreases perf when running a large number of cells, I think this is acceptable (200 cells in 10s is accpetable with this architecture),

[DonJayamanne]

Duplicate of #6941

[DavidKutu]

the new time is around 12 seconds