Disable other extensions for debugging and testing

This change disables other extensions during debugging and running tests.

Documentation: https://code.visualstudio.com/api/working-with-extensions/testing-extension#disabling-other-extensions-while-debugging

The main reason for the change is to make sure that our CI (where we don't have any additional extensions) behaves the same way as our local version.

The potential drawback is that we might miss some UI clashes with other extensions. This drawback is hypothetical, I can't give any concrete example of such a clash.

Closes #122 (closed)