Fix "Open folder" from vscode.dev UI toolbar menu (current workaround: modify URL manually)

[tbombach]

Depends on: #1939

This is because the query parameters are not preserved by vscode.dev when opening a different folder.

[lebaro-msft]

Another (likely related) issue: if you use the url to change the folder, the source control isn't recognizing the folder you are in so it doesn't work anymore