Jupyter notebooks should obey files.trimTrailingWhitespace rule

[phil-chp]

Hello!

This issue has in fact already been discussed over a year ago: #151982, but didn't get enough traction, so I'm trying again.

I understand how this feature would have been missed, but the fact that I'm able to open the command palette and execute manually Trim Trailing Whitespace indicated this is a sort of bug.

So the idea is that when we have trailing whitespace characters in a Jupyter Notebook, and in our VScode settings we have any of the following rules:

{
    "files.trimTrailingWhitespace": true,
    "files.trimFinalNewlines": true,
    "files.insertFinalNewline": true,
}

These rules should apply to the Notebook, but this doesn't work.

[rebornix]

This is a duplicate of #181905 and we have it on our iteration plan now.