Positionable: Common interface for canvas items (#256)

* Add Positionable interface to canvas elements

* Add group resizeTo children

Refactor out duplicated code from Node

* Remove redundant "is_selected" check

* Improve measure pass - interface, caching

Node bounds once per render
Cached results

* Use cached bounds for repeat canvas calls

- Removes margin param from getNodeOnPos
- Removes margin param from getGroupOnPos
- Hitboxes now uniform for render / mouse features
- Simplifies code

* nit - Refactor

* Fix top-left edge of hitbox missing

* Add ID to groups

src/interfaces.ts

@@ -1,5 +1,5 @@
 import type { ContextMenu } from "./ContextMenu"
-import type { LGraphNode } from "./LGraphNode"
+import type { LGraphNode, NodeId } from "./LGraphNode"
 import type { LinkDirection, RenderShape } from "./types/globalEnums"
 import type { LinkId } from "./LLink"
 
@@ -12,6 +12,35 @@ export type NullableProperties<T> = {
 
 export type CanvasColour = string | CanvasGradient | CanvasPattern
 
+export interface Positionable {
+    id: NodeId | number
+    /** Position in graph coordinates.  Default: 0,0 */
+    pos: Point
+    /** true if this object is part of the selection, otherwise false. */
+    selected?: boolean
+
+    readonly children?: ReadonlySet<Positionable>
+
+    /**
+     * Adds a delta to the current position.
+     * @param deltaX X value to add to current position
+     * @param deltaY Y value to add to current position
+     * @param skipChildren If true, any child objects like group contents will not be moved
+     */
+    move(deltaX: number, deltaY: number, skipChildren?: boolean): void
+
+    /**
+     * Cached position & size as `x, y, width, height`.
+     * @readonly See {@link move}
+     */
+    readonly boundingRect: ReadOnlyRect
+
+    /** Called whenever the item is selected */
+    onSelected?(): void
+    /** Called whenever the item is deselected */
+    onDeselected?(): void
+}
+
 export interface IInputOrOutput {
     // If an input, this will be defined
     input?: INodeInputSlot