CodeViewer: remove codemirror dependency and implement decorators by hand

[danilowoz]

Currently, the CodeViewer component uses the same component from CodeEditor to highlight and set the decorators on the code block. However, as this component might be static and it's already read-only, we could try to remove the CodeMirror dependency in order to turn it lightweight and free of dependency.

As a result, this would avoid the initialization a new CodeMirror instance on every new codeblock, and turn the implementation way simple.

TODO:

• Split CodeViewer and CodeMirror in two;
• Implement syntax-highlight;
• Implement decorators;

Reference: reactjs/react.dev#5110