Navigation Block: Render nav items from __unstableLocation even if there is content inside the block.

[scruffian]

Description

At present if a Navigation block has content, the __unstableLocation attribute will be ignored. This makes it impossible to specify a default for the block and also allow users update the menu from the Classic dashboard.

Instead, if the block has an __unstableLocation defined and there is a menu at that location, the contents of the block should be ignored.

When the user edits the navigation block then the __unstableLocation attribute should be removed, as at present.

Step-by-step reproduction instructions

1. Create a navigation block with a site logo inside and an __unstableLocation

<!-- wp:navigation {"__unstableLocation":"primary"} -->
<!-- wp:site-logo /-->
<!-- /wp:navigation -->

2. Notice that the site logo will always appear, even if I have a menu set at my "primary" location.

Screenshots, screen recording, code snippet

No response

Environment info

• Tested with Blockbase and emptytheme

Please confirm that you have searched existing issues in the repo.

Yes

Please confirm that you have tested with all plugins deactivated except Gutenberg.

Yes