Fix dragging Vue nodes into canvas from library (#8118)

## Summary

Updates the node preview rendering to use the same app context as the
main app so it can access the same plugins

## Changes

Assigns manually created vnode app context to the current instances
context

## Review Focus

This is using somewhat advanced/almost-internal Vue functionality,
however I couldn't come up with a better alternative that didn't require
recreating an entirely new app and re-registering all dependencies or
redoing how draggable node previews are done.
The draggable image needs to be rendered synchronously, so rendering a
node in the active app and capturing that isn't possible to guarantee to
be done synchronously (afaik - suggestions welcome)

┆Issue is synchronized with this [Notion
page](https://www.notion.so/PR-8118-Fix-dragging-Vue-nodes-into-canvas-from-library-2eb6d73d365081a0a956d8280e009592)
by [Unito](https://www.unito.io)

src/components/sidebar/tabs/nodeLibrary/NodeBookmarkTreeExplorer.vue

@@ -22,7 +22,15 @@
 </template>
 
 <script setup lang="ts">
-import { computed, h, nextTick, ref, render, watch } from 'vue'
+import {
+  computed,
+  getCurrentInstance,
+  h,
+  nextTick,
+  ref,
+  render,
+  watch
+} from 'vue'
 import { useI18n } from 'vue-i18n'
 
 import FolderCustomizationDialog from '@/components/common/CustomizationDialog.vue'
@@ -41,6 +49,8 @@ import type {
   TreeNode
 } from '@/types/treeExplorerTypes'
 
+const instance = getCurrentInstance()!
+const appContext = instance.appContext
 const props = defineProps<{
   filteredNodeDefs: ComfyNodeDefImpl[]
   openNodeHelp: (nodeDef: ComfyNodeDefImpl) => void
@@ -154,6 +164,7 @@ const renderedBookmarkedRoot = computed<TreeExplorerNode<ComfyNodeDefImpl>>(
         },
         renderDragPreview(container) {
           const vnode = h(NodePreview, { nodeDef: node.data })
+          vnode.appContext = appContext
           render(vnode, container)
           return () => {
             render(null, container)