"All of DSpace" menu in nav bar remains open and obscures site visibility when navigating by keyboard only

[hostle83]

Describe the bug

Once opened by keyboard-only users, the "All of DSpace" menu in the nav bar remains open even when moving to other elements on the site and obscures visibility:

To Reproduce
Steps to reproduce the behavior:

1. Go to the sandbox or demo site
2. Use keyboard only to navigate to the All of DSpace menu item in the nav bar
3. Open the menu by pressing Enter on keyboard
4. Move out of the menu by pressing tab (multiple times, first have to move through the menu)

Expected behavior
The "All of DSpace" menu should close automatically once having moved out of it

Related work
This could potentially be a related issue: #3021

[atarix83]

@tdonohue @hostle83

4science is interested in working on this task and the related one #3021

Estimation is about 6h

[alexandrevryghem]

We also discovered that the navbar could also not correctly expand with some screenreaders and I created a fix for this last week. I was planning on opening a PR for that this week but there were still a few minor tweaks that I was going to make this week 😅 . That PR completely refactors the way the expandable menu section works and also already fixes this issue 🤷

[tdonohue]

@alexandrevryghem and @atarix83 : Since @alexandrevryghem already has a fix, then I'll reassign this to his plate.

I know that @atarix83 is simply trying to help claim "accessibility" tickets, as the DSpace Steering has prioritized fixing them using money obtained via the DSpace Development Fund.

Therefore, @alexandrevryghem , if there are other "accessibility" tickets that you've already fixed / have fixes for, please ask to claim them soon. That'll ensure that we don't accidentally do duplicative work.