Move vscode builtin production from yarn to npm

[rschnekenbu]

Migrate the package manager of VS Code from yarn to npm
Also updates to vscode subrepo to 1.94.2, as this is the first version to rely on npm.

fixes #131

contributed on behalf of STMicroelectronics

[tsmaeder]

@rschnekenbu is there documentation that needs to be updated with this change?

[rschnekenbu]

@tsmaeder, probably some README or how-to-build documentation to update, indeed. I will update this PR

[rschnekenbu]

@tsmaeder, I updated the documentation, some commands now relying on npm rather than yarn on vscode repo.
This vscode-builtin-extensions repository still uses yarn v1 of course, so many of the building commands and all publishing ones are still yarn based.

I took also the opportunity to update the vscode commit ref to tag 1.94.2 (current latest release on 1.94 stream). I also updated some part of the documentation that had some markdown formatting issues or warnings.