Summary:
It can be hard to find changes, even when highlighted, in a table with many rows. This diff replaces long sequences of unchanged rows with a row containing "..."s.
With daff, I found that it is important to do this for sequences of unchanged columns also, but not tackling that yet.
Test Plan: added test
Reviewers: dsagal
Reviewed By: dsagal
Differential Revision: https://phab.getgrist.com/D2666
c387fc4bce