Add support for dynamic widgets (#6661)

Adds support for "dynamic combo" widgets where selecting a value on a
combo widget can cause other widgets or inputs to be created.


![dynamic-widgets_00001](https://github.com/user-attachments/assets/c797d008-f335-4d4e-9b2e-6fe4a7187ba7)

Includes a fairly large refactoring in litegraphService to remove
`#private` methods and cleanup some duplication in constructors for
subgraphNodes.

┆Issue is synchronized with this [Notion
page](https://www.notion.so/PR-6661-Add-support-for-dynamic-widgets-2a96d73d3650817aa570c7babbaca2f3)
by [Unito](https://www.unito.io)

---------

Co-authored-by: Alexander Brown <drjkl@comfy.org>

src/lib/litegraph/src/LGraphNode.ts

@@ -848,15 +848,13 @@ export class LGraphNode
       }
 
       if (info.widgets_values) {
-        const widgetsWithValue = this.widgets.filter(
-          (w) => w.serialize !== false
+        const widgetsWithValue = this.widgets
+          .values()
+          .filter((w) => w.serialize !== false)
+          .filter((_w, idx) => idx < info.widgets_values!.length)
+        widgetsWithValue.forEach(
+          (widget, i) => (widget.value = info.widgets_values![i])
         )
-        for (let i = 0; i < info.widgets_values.length; ++i) {
-          const widget = widgetsWithValue[i]
-          if (widget) {
-            widget.value = info.widgets_values[i]
-          }
-        }
       }
     }
 
@@ -1652,6 +1650,19 @@ export class LGraphNode
     this.onInputRemoved?.(slot, slot_info[0])
     this.setDirtyCanvas(true, true)
   }
+  spliceInputs(
+    startIndex: number,
+    deleteCount = -1,
+    ...toAdd: INodeInputSlot[]
+  ): INodeInputSlot[] {
+    if (deleteCount < 0) return this.inputs.splice(startIndex)
+    const ret = this.inputs.splice(startIndex, deleteCount, ...toAdd)
+    this.inputs.slice(startIndex).forEach((input, index) => {
+      const link = input.link && this.graph?.links?.get(input.link)
+      if (link) link.target_slot = startIndex + index
+    })
+    return ret
+  }
 
   /**
    * computes the minimum size of a node according to its inputs and output slots