Snap everything to grid (#315)

* Implement snap to grid

- Moves positioning logic to LGraph
- Simplifies code
- Adds Pointer API to alt-clone node
- Removes always_round_positions, replaced by always snap to grid (default size is 1 when always snapping)

Fix refator error

* Fix group items snapped without group

* Allow snapping of all items

- Add snapToGrid to Positionable
- Impl. on all types
- Deprecated: alignToGrid is now a wrapper

* Fix test import alias, update expectations

* Prevent desync of before / after change events

Adds ability to perform late binding of finally() during drag start.

* nit - Refactor

* Fix unwanted snap on node/group add

* nit - Doc

* Add shift key state tracking for snap to grid

Private impl., no state API as yet.

* Add snap guides rendering

Nodes, reroutes

* Optimisation - reroute rendering

 Fixes exponential redraw

* Add snap guidelines for groups

test/__snapshots__/litegraph.test.ts.snap

@@ -134,7 +134,6 @@ LiteGraphGlobal {
   "allow_multi_output_for_events": true,
   "allow_scripts": false,
   "alt_drag_do_clone_nodes": false,
-  "always_round_positions": false,
   "auto_load_slot_types": false,
   "auto_sort_node_types": false,
   "catch_exceptions": true,