Add support for dragging in multiple workflow files at once (#8757)

## Summary

Allows users to drag in multiple files that are/have embedded workflows
and loads each of them as tabs.
Previously it would only load the first one.

## Changes

- **What**: 
- process all files from drop event
- add defered errors so you don't get errors for non-visible workflows

┆Issue is synchronized with this [Notion
page](https://www.notion.so/PR-8757-Add-support-for-dragging-in-multiple-workflow-files-at-once-3026d73d365081c096e9dfb18ba01253)
by [Unito](https://www.unito.io)

src/composables/usePaste.test.ts

@@ -201,11 +201,10 @@ describe('pasteImageNodes', () => {
 
     const file1 = createImageFile('test1.png')
     const file2 = createImageFile('test2.jpg', 'image/jpeg')
-    const fileList = createDataTransfer([file1, file2]).files
 
     const result = await pasteImageNodes(
       mockCanvas as unknown as LGraphCanvas,
-      fileList
+      [file1, file2]
     )
 
     expect(createNode).toHaveBeenCalledTimes(2)
@@ -217,11 +216,9 @@ describe('pasteImageNodes', () => {
   })
 
   it('should handle empty file list', async () => {
-    const fileList = createDataTransfer([]).files
-
     const result = await pasteImageNodes(
       mockCanvas as unknown as LGraphCanvas,
-      fileList
+      []
     )
 
     expect(createNode).not.toHaveBeenCalled()

src/composables/usePaste.ts

@@ -96,7 +96,7 @@ export async function pasteImageNode(
 
 export async function pasteImageNodes(
   canvas: LGraphCanvas,
-  fileList: FileList
+  fileList: File[]
 ): Promise<LGraphNode[]> {
   const nodes: LGraphNode[] = []