Improve long page editing performance (#3855)

* Remove expensive parsing when saving files

* Add limit to page blocks query

* Don't collapse block's body to make it compatible with other tools

* Alert if there're unsaved changes when switching graphs

* DB schema migration for :block/collapsed? from it's property

Co-authored-by: Andelf <andelf@gmail.com>

src/main/frontend/format/block.cljs

@@ -603,6 +603,9 @@
 
                                 (seq (:properties-order properties))
                                 (assoc :properties-order (:properties-order properties)))
+                        block (if (get-in block [:properties :collapsed])
+                                (assoc block :collapsed? true)
+                                block)
                         block (-> block
                                   (assoc-in [:meta :start-pos] start_pos)
                                   (assoc-in [:meta :end-pos] last-pos)