This avoids an issue where in a many-buffer multi-buffer, each modified
buffer could complete its recalc independently, causing a cascade of
repeated notifies
Now all recalcs started at the same time must complete before
A: Starting another recalc pass
B: The master notify occurring
Each buffer can still show its new diff if something else triggers it
to notify earlier, this is desirable and does not have the same negative
effects as the notify cascade as those re-layouts would need to happen
anyway
Co-Authored-By: Max Brunsfeld <max@zed.dev>
