Nav Sidebar: Improve arrow key navigation and focus

[getdave]

When moving inside a navigation item with the Arrow keys, focus doesn't follow the visual order of the buttons. I can only focus "Move up" and "Move down" by focusing the "Options" button first, and then moving back with Left Arrow. Not sure what's happening there, but focus order and markup order aren't matching.

See #39290.

As suggested there let's improve the navigation using arrow keys.

[tellthemachines]

As @talldan suggested here, we could also temporarily hide the movers until this problem is fixed. We shouldn't ship the navigation sidebar in 6.0 with pending a11y issues.

[talldan]

I'm getting a bit nervous about this with the release around the corner, so I've made a PR that hides the movers - #40039.

[getdave]

I'm getting a bit nervous about this with the release around the corner, so I've made a PR that hides the movers - #40039.

Apologies I've been sidetracked fixing bugs in the Nav block itself.

[github-actions]

Hi,
This issue has gone 180 days without any activity. This means it is time for a check-in to make sure it is still relevant. If you are still experiencing this issue with the latest versions, you can help the project by responding to confirm the problem and by providing any updated reproduction steps.
Thanks for helping out.

[getdave]

Still valid.