Support an option to 'dim` the un-annotated code by default (to draw attention to the annotated code). If the reader mouse's over the code block, activate all the code. 

For example, default mode:

<img width="1224" alt="Screenshot 2023-03-27 at 7 27 05 PM" src="https://user-images.githubusercontent.com/261654/228089396-adaf1faf-407b-4e2c-8a10-369743a8995c.png">

dragonstyle
2023-03-27T23:29:00Z
dragonstyle
enhancement
v1.4
open
Support Default Highlighting Code in Code Annotations
https://github.com/quarto-dev/quarto-cli/issues/4989