When drilling down into a code insights data point, we generate a diff search for the difference between that data point and the point before it. This is not ideal for many reasons:

1. It is somewhat confusing semantics. You don't see what the data point represents, you only see the diff
2. Many code insights searches cannot actually be represented as a diff search
3. The query rewriting has been the source of a bunch of different bugs
4. Diff search is slow

Instead, we want to change the behavior to drill down into a search at the commit that data point represents.

### Related issues
- [ ] https://github.com/sourcegraph/sourcegraph/issues/60686
- [ ] https://github.com/sourcegraph/sourcegraph/issues/58906