[Side panel] File System Access permission prompt does not show after picking a folder

[Jaifroid]

Tested with my app https://pwa.kiwix.org -- this is ideal for the side panel, as it is a reference tool able to access a library of archives stored on the user's hard drive (e.g. a full offline copy of Wikipedia). Access is via the File System Access API.

Unfortunately, the requisite permissions prompt is not displayed to the user when the app is in the side panel and the user picks a directory. Permission is not granted, but there is no indication to the user about what has happened.

Drag-and-drop does still work, so I was able to test the app. Apart from this one issue, the app works very well with the edge_side_panel key enabled.