Mark diff chunks as "viewed" rather than entire files

[sdwatkinsdev]

Select Topic Area

Product Feedback

Body

I'd like to be able to mark each diff chunk as "viewed", not just whole-file granularity. Just like when I use git add -p to build a commit by chunks rather than by whole files. This will help a ton in situations where there are simple changes I can quickly check off (collapsing them from the larger diff) intermingled with tricky/questionable stuff I want to come back to.

To minimize cheese relocation factor, we can keep the file-level "Viewed" checkbox and its UX nearly unchanged, but add the behavior of toggling the "Viewed" state for each chunk within.

Similar to this previous suggestion, but not sure if it's identical. That request mentions "mark viewed" for custom line ranges, like comments, which may be more than I need. Although I agree it would be nice to have a "split" option (concept again stolen from git add -p).