Right sidebar has initial focus when open upon page visit

[kulmann]

Describe the bug

We now persist the open/closed state of the right sidebar in the localStorage of the browser and restore that state on the next visit (has been implemented in #10612 ).
In that case (open sidebar upon first page load) the right sidebar has the initial focus. That's an accessibility violation.

Steps to reproduce

1. Open right sidebar anywhere
2. Close the browser
3. Reopen the browser

Expected behavior

There is no initial focus set. First TAB always jumps to the hidden button which let's the user navigate to the <main> content.

Actual behavior

Right sidebar is initially focussed. First TAB jumps to the X button to close the right sidebar.