[BITV] Fix left sidebar from a11y perspective

[szaimen]

Two issues:

1. Toggle to close the sidebar is not visible on small displays:

2. Sidebar does not feature focus trap

Aufzeichnung.2023-10-11.145807.mp4

Also see the discussion in #36964 (comment) and below

[JuliaKirschenheuter]

Please keep in mind (Photos): once sidebar is closed it is not possible to open it again

[szaimen]

Please keep in mind (Photos): once sidebar is closed it is not possible to open it again

Needs a vue library update then iirc...

[szaimen]

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        ![Peek 2023-10-20 10-00](https://user-images.githubusercontent.com/6078378/276863574-c92c7b42-5c22-4d03-af1e-d2135dae1f1a.gif)
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   [ ![Peek 2023-10-20 10-00](https://user-images.githubusercontent.com/6078378/276863574-c92c7b42-5c22-4d03-af1e-d2135dae1f1a.gif) ](https://user-images.githubusercontent.com/6078378/276863574-c92c7b42-5c22-4d03-af1e-d2135dae1f1a.gif)
  
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        ![Peek 2023-10-20 10-00](https://user-images.githubusercontent.com/6078378/276863574-c92c7b42-5c22-4d03-af1e-d2135dae1f1a.gif)
      ](https://user-images.githubusercontent.com/6078378/276863574-c92c7b42-5c22-4d03-af1e-d2135dae1f1a.gif)
    
    
      
        
          
        
        
          
          
        
      
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Needs a vue library update then iirc...

WIP here: nextcloud/photos#2111