Fix navigation menu insertion issues

[talldan]

Description

On #18100 I was having some issues with insertion in the nav block:

• the new __experimentalGetAllowedBlockTypes selector was throwing an error when blockListSettings didn't contain a setting for a particular block. Not entirely sure why this happens.
• An undefined destinationRootClientId prop was being used to get the insertion index. This would mean the block would often be insterted in the wrong place.

The fixes:

• Update the selector to be more like the hasInserterItems selector.
• Use the already defined rootClientId prop.

How has this been tested?

1. Add a navigation block
2. Add menu items to the nav block
3. Expect that the menu items are added correctly

Types of changes

Bug fix (non-breaking change which fixes an issue)

Checklist:

• My code is tested.
• My code follows the WordPress code style.
• My code follows the accessibility standards.
• My code has proper inline documentation.
• I've included developer documentation if appropriate.

[draganescu]

This fixes inserting in the wrong position for the new "smart" appender. It is finally smart :O)

[draganescu]

It's interesting that we've seen this after merge as in my local testing I wasn't getting any issues, visual or console.