Refactor gutenberg_initialize_editor function and remove block_editor_preload_data filter

[anton-vlasenko]

What problem does this address?

This issue is a follow-up to #24642.
We've added block_editor_preload_data filter to the gutenberg_initialize_editor function.
This filter is only needed to provide data for the createMenuPreloadingMiddleware.
It's not the best solution because we don't want to add filters whose only task is to solve a specific (single) issue.
We can do better.
We need to refactor gutenberg_initialize_editor to not use that filter.

What is your proposed solution?

Load the data needed for the createMenuPreloadingMiddleware sideways, somewhere inside the gutenberg_navigation_init function and remove the block_editor_preload_data filter.