At first, I found it less convenient than the previous way, but:
- you will see the Library button at the top right of XCode, above Inspectors, on the left of Inspectors buttons).
And this pull down button is contextual, after long press, depending you are in
- IB : shows Object Library or Media Library
- In code: Snippet or Media Library
But I don't know where File Template Library has gone !
A good point : it is possible to move the window to avoid travelling a long time with the object, and to resize the window.
To keep this panel open after drag: just option-drag, and the window stays open. Great !
So, at the end, this design appear more flexible.