There are two different UI in this PR: `comparing` and `viewing` mode.
- For `comparing`, the user would be shown two separate date. It uses the `UpdateRange` object and this PR adds a timestamp to both `fromV` and `toV` of the object type.
- For `viewing`, the user would only be shown one date since `viewing` mode means viewing a specific update version.
Some other notable changes:
- Move `diff` state to `diff-view.tsx`, which contains `main.tsx` (main editor history view) and `toolbar.tsx` as its children
- refactor `autoSelectFile` by passing `updateRange.toV` directly
- refactor `updateIsSelected` by passing an object that contains `fromV` and `toV` instead of passing `update
There's also a cypress test for both the `viewing` mode and `comparing` mode in this PR.
GitOrigin-RevId: ba54f073f3479c55a39eb6b2932ea7faff78dddc
