message: Compress number of changes needed to undo/redo
  Unbeknownst to me, our diff engine (diff-match-patch) can combine changes to either be more intuitive for humans or to be more efficient for machines. We now make it do the latter, which results in fewer blocking calls when undoing and redoing.
diff: @@ -548,6 +548,7 @@ export class HistoryTracker {
  // them to call addChange manually, I guess...
  const diffs = diffEngine.diff_main(this.previousDocumentState.text, newText);
  + diffEngine.diff_cleanupEfficiency(diffs);
  /*
  this.historySteps.push(new HistoryStep({
  