Spreadsheet: Improve sheet update efficiency

There's no need to leave the cell dirty when not updating it, and
there's definitely no need to update the cells as we're selecting them.
This makes navigating a sheet and selecting cells significantly faster
as we no longer update unrelated cells just because they appear to have
a cyclic update dependency :^)

Applications/Spreadsheet/SpreadsheetView.cpp

@@ -86,6 +86,10 @@ void InfinitelyScrollableTableView::mousemove_event(GUI::MouseEvent& event)
         if (!index.is_valid())
             return TableView::mousemove_event(event);
 
+        auto& sheet = static_cast<SheetModel&>(*model).sheet();
+        sheet.disable_updates();
+        ScopeGuard sheet_update_enabler { [&] { sheet.enable_updates(); } };
+
         auto holding_left_button = !!(event.buttons() & GUI::MouseButton::Left);
         auto rect = content_rect(index);
         auto distance = rect.center().absolute_relative_distance_to(event.position());