Fix output of jupyter notebooks saved in VSCode
What does this MR do?
VSCode uses the newer NBFormat Version 4.1, which allows the output text entry to be a simple string.
The function rawCode assumed NBFormat Version 3.2, which requires the output.text object to be an array.
This commit adds a special handling if the type of output.text is a
string, then we don't need to use join() and can just return the
string.
Fixes: #212837 (closed)
Screenshots
Output of VSCode generated jupyter notebook now renders correctly
