Explore prompt to convert page link on drop instead of drag

[draganescu]

What problem does this address?

Currently, after #48723, when a page list is a child of a navigation block, dragging a page list child in the navigation block's inspector prompts the user immediately to convert the page list block to a list of navigation link blocks.

This creates an unexpected modal before the user effects their intent and so the user is in a state where they have a chip attached to their pointer on top of the modal. This is weird and it creates uncertainty on results of next step.

What is your proposed solution?

Let's explore triggering the modal when the page list item is dropped. There are two advantages of this:

1. We show the modal once the user has their focus on "what's next" and we don't interrupt their flow
2. We could know the drop target and, indifferent of what they choose following the prompt, we commit their action (basically the reordering).