Editor: Fixed selected object unselected when recovering

[ycw]

The issue: The selected scene object in outliner becomes unselected when recovering

To reproduce:

1. Select a scene object in outliner
2. Refresh the page
3. You should see nothing is being selected in outliner

This cause: "Restoring selected object" editor.selectByUuid() should follow "Restoring the editor" editor.fromJSON(), however, editor.fromJSON() returns a promise which ... isn't be awaited ... , so the order is reversed and failed as expected.

This PR fixed that by simply awaiting the editor.fromJSON() .

[ycw]

Clarify that this PR can only restore selected state if selected object is a scene object. i.e. If users selected default Camera or Scene, there will be nothing auto-selected in outliner after restoring.