[FEATURE]: Mention popup quick-open shortcuts for files and directories #16810

Feature hasn't been suggested before.

• I have verified this feature I'm about to request hasn't been suggested before.

Describe the enhancement you want to request

It would be highly beneficial to have quick-open shortcuts available when navigating the @ mention popup menu for files and directories. This enhancement would improve the workflow by allowing users to quickly access the relevant files or their containing folders without breaking focus.

Specifically, we'd like to see the following functionality:

• Open in External Editor: When hovering over a file in the @ mention view, pressing Ctrl+X should quickly open that file in the configured external editor.
• Open in OS File Manager: When hovering over a directory (or a file's containing directory) in the @ mention view, pressing Alt+O should open that location in the OS file manager.

Discoverability:
To ensure users are aware of these shortcuts, a footer or small tip indicating this functionality should be added at the bottom of the mention popup.