Allow copy-pasting code from the Vitest UI

[rossng]

Clear and concise description of the problem

At the moment it isn't possible to copy-paste code from the module graph browser (and probably other places using the CodeMirror renderer). This would be useful for debugging: e.g. when comparing the compiled output with different settings.

Suggested solution

Enable copying text from all code blocks in the Vitest UI.

Alternative

N/A

Additional context

Noticed this during the discussion on #2242

Validations

• Follow our Code of Conduct
• Read the Contributing Guidelines.
• Read the docs.
• Check that there isn't already an issue that request the same feature to avoid creating a duplicate.