fix: file conflict resolution

[briangregoryholmes]

• Updates conflict detection logic to be less intrusive
• Updates alert copy
• Adds diff/merge view
• Adds saving/error indicators to sidebar and save button

[nishantmonu51]

@briangregoryholmes : Is this ready for review ?

[ericpgreen2]

Overall, feels good!

UXQA:

1. With autosave disabled, I add text (e.g. "abc"), then delete that same text, then attempt to save the file (the "unsaved changes" indicator was showing), it fails to save. (Jam)
2. After I accept remote changes, I see the red exclamation point.
   

@mindspank could we call you the Product Owner of the code editor, and can you give this a look too?

[briangregoryholmes]

All fixed. I also extended the autosave debounce to 650ms, which feels better to me.

[ericpgreen2]

The "Accept current" button is unresponsive for me: Jam

[ericpgreen2]

Approving so you can merge at your discretion