Refactor gutenberg_initialize_editor function and remove block_editor_preload_data filter

[anton-vlasenko]

Description

This PR is a follow-up to #24642.
Fixes #35803
We've added block_editor_preload_data filter to the gutenberg_initialize_editor function in the scope of #35402.
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.

How has this been tested?

1. Open the navigation page (wp-admin/admin.php?page=gutenberg-navigation).
2. Make sure that the first menu from the list of menus is selected as the current menu.
3. Make sure there is only 1 fetch/XHR request (see the screenshot below), meaning that the preloading is working.

Screenshots

Screenshots

Types of changes

New feature

Checklist:

• My code is tested.
• My code follows the WordPress code style.
• My code follows the accessibility standards.
• I've tested my changes with keyboard and screen readers.
• My code has proper inline documentation.
• I've included developer documentation if appropriate.
• I've updated all React Native files affected by any refactorings/renamings in this PR (please manually search all *.native.js files for terms that need renaming or removal).

[anton-vlasenko]

@TimothyBJacobs @spacedmonkey
Could you please review this pull request, so we don't ship Gutenberg with the block_editor_preload_data filter?

[TimothyBJacobs]

Thanks this looks great!