Make the UI make sense for MCQ assessments

[heyzec]

When detected to be within VS Code, the frontend always hides the left part of the page to hide the editor. This does not make sense for MCQ assessments.

1. Start the WebView, navigate to an MCQ assessment (e.g. Sorting Things Out)
2. The VS Code editor should be hidden. The MCQ options should appear.

[shirsho-12]

Currently, if a question is viewed, the following takes place:

• A JS file named assessment{id}_{q_num}.js is opened on the code editor. The file always contains 3 header lines

// PREPEND -- DO NOT EDIT

// END PREPEND

• Only the header is shown in the code if the question is an MCQ.

TODO: close the editor and open an MCQ panel on the left.

[heyzec]

This PR might be useful to understand how the frontend hides the editor.
source-academy/frontend#3080