Fix `Global::gt` and rename it to `changed_since`

A false negative return value of `gt` was preventing guests' multibuffers from
syncing correctly.

Co-Authored-By: Nathan Sobo <nathan@zed.dev>
e5faaeb2f2Max Brunsfeld committed on 1/6/2022, 1:36:12 AMparent4b22e49
4 files changedLine totals unavailable