Moving nested blocks out of their block container is not possible with keyboard only

[tellthemachines]

Describe the bug

When a block has nested blocks, such as columns, or sub-navigation menus, a nested block can't be moved out of its block container, whether up one level, or into a different container, with the keyboard only.

With the Navigation block there is the added complication of toolbars being fixed to the top of the block, so it isn't even possible to drag blocks between levels of nesting.

This is a blocker for the experimental use of the Navigation block in /nav-menus.php, because the current menus page provides the ability to drag and drop blocks and move them with the keyboard in any direction.

One possible avenue for exploration is having drag/drop/move functionality in the block navigator: #18014, #21372.

Related issues: #20955, #21391, #20078.

To reproduce
Steps to reproduce the behavior:

1. Go to '...'
2. Click on '....'
3. Scroll down to '....'
4. See error

Expected behavior
A clear and concise description of what you expected to happen.

Screenshots
If applicable, add screenshots to help explain your problem.

Editor version (please complete the following information):

• WordPress version: [e.g: 5.3.2]
• Does the website has Gutenberg plugin installed, or is it using the block editor that comes by default? [e.g: "gutenberg plugin", "default"]
• If the Gutenberg plugin is installed, which version is it? [e.g., 7.6]

Desktop (please complete the following information):

• OS: [e.g. iOS]
• Browser [e.g. chrome, safari]
• Version [e.g. 22]

Smartphone (please complete the following information):

• Device: [e.g. iPhone6]
• OS: [e.g. iOS8.1]
• Browser [e.g. stock browser, safari]
• Version [e.g. 22]

Additional context

• To report a security issue, please visit the WordPress HackerOne program: https://hackerone.com/wordpress.

[tellthemachines]

Fixed by #22453.