Keyboard in block navigation editable text not working correctly

[talldan]

Describe the bug
A combination of #18014 and #22210 being worked on in parallel seems to have resulted in some issues keyboard navigating around block navigation on the experimental Navigation page:

• The contenteditable (RichText) used in block navigation isn't managed as part of the roving tab index system
• Horizontal arrow keys aren't usable for moving the caret within the contenteditable

To reproduce
Steps to reproduce the behavior:

1. Enable and visit the experimental navigation page (wp-admin/admin.php?page=gutenberg-navigation)
2. Add a navigation block with several links
3. Tab into block navigation and use arrow keys to move to a navigation link's editable text
4. Try to use horizontal arrow keys while the caret is within some text
5. Observe that focus is moved out of the contenteditable
6. Arrow key back to a contenteditable
7. Try using tab or shift+tab to tab out of block navigation
8. Observe that tab often navigates to another contenteditable.

Expected behavior

• Arrow keys can be used to edit text, only moving to another element when at boundaries of text.
• Block navigation has a single tab stop.

[talldan]

This should have been closed by #22885 and also that the input is not longer active in List View.