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

src/CanvasPointer.ts

@@ -68,8 +68,11 @@ export class CanvasPointer {
   /** The last pointerup event for the primary button */
   eUp: CanvasPointerEvent | null = null
 
-  /** If set, as soon as the mouse moves outside the click drift threshold, this action is run once. */
-  onDragStart?(): unknown
+  /**
+   * If set, as soon as the mouse moves outside the click drift threshold, this action is run once.
+   * @param pointer This pointer instance.  Permits actions such as late binding of the finally() callback.
+   */
+  onDragStart?(pointer: this): unknown
 
   /**
    * Called on pointermove whilst dragging.
@@ -232,7 +235,7 @@ export class CanvasPointer {
 
   #setDragStarted(): void {
     this.dragStarted = true
-    this.onDragStart?.()
+    this.onDragStart?.(this)
     delete this.onDragStart
   }