Add auto-fix diagnostics with AI feature

[nichochar]

Ability to one click get a diff with a fix for Diagnostics.

I did not have designs for this.
Happy to iterate if you have suggestions, but I think we can merge for a couple of reasons:

• good to get the feature out to start testing it and using it
• it's hidden in the diagnostics tab

I reused the purple color which Justin suggested we use for the AI features. I think this is a good idea, although it needs some improvements in dark mode.

I have QA'd the feature a little but it's hard to know what accuracy the prompt has without more rigorous eval testing.

Video of the experience

CleanShot.2024-08-08.at.17.05.18.mp4

Notes

• The state on the code cell is getting intense. Refactoring leads to bugs, which is a smell
• I reused a websocket message for the diff mechanism. Did not add a new message because it felt that it's the same mechanism of the AI suggesting a diff. Had to add a tiny bit of state since the behavior on revert is slightly different for a diagnostics fix vs an 'ai edit'.
• Renamed some of the state vars in code.tsx, which I think is an improvement