Fix vue node slot position calculation (#7877)

## Summary

Fix slot position for Vue nodes using LiteGraph calculation

Fixes #7446

## Changes
- Updated getInput/OutputPos to call getSlotPosition which handles
positions for both LiteGraph & Vue nodes correctly
- Add regression test

┆Issue is synchronized with this [Notion
page](https://www.notion.so/PR-7877-Fix-vue-node-slot-position-calculation-2e16d73d365081219afef0e4ebfb0620)
by [Unito](https://www.unito.io)

---------

Co-authored-by: github-actions <github-actions@github.com>

browser_tests/fixtures/VueNodeHelpers.ts

@@ -163,4 +163,14 @@ export class VueNodeHelpers {
       incrementButton: widget.getByTestId('increment')
     }
   }
+
+  /**
+   * Enter the subgraph of a node.
+   * @param nodeId - The ID of the node to enter the subgraph of. If not provided, the first matched subgraph will be entered.
+   */
+  async enterSubgraph(nodeId?: string): Promise<void> {
+    const locator = nodeId ? this.getNodeLocator(nodeId) : this.page
+    const editButton = locator.getByTestId('subgraph-enter-button')
+    await editButton.click()
+  }
 }