Unpinned admin sidebar can remain expanded after cursor is moved out

[ybnd]

Describe the bug

Once in a while, the admin sidebar "sticks" in the expanded state after the cursor is moved out.

Steps to reproduce the behavior:

1. Log in for the admin sidebar to show up
2. Hover over the sidebar until it expands
3. Open at least one expandable menu section
4. Move the cursor out of the sidebar, but don't click anywhere so it doesn't lose focus
   • You'll see that the sidebar remains open
   • You can scroll the page and interact with other "hoverable" elements, and the sidebar will remain open
   • You can even move the cursor out of the browser window
5. Click anywhere
   • The sidebar will close

Expected behavior

There should be a general timeout to ensure the admin sidebar closes after a while once the cursor is moved out.

[alanorth]

@ybnd I have seen the top menu bar do this as well. Menu items with dropdowns like "All of DSpace" can get stuck too. We have three menu items with dropdowns so it is more likely to be triggered. As far as I recall, both these menus use the same implementation so might be affected by the same bug.

[alexandrevryghem]

I already fixed that behaviour in #3581 for the PUBLIC menus with the HoverOutsideDirective. The same directive could be used to fix this issue.