Site Editor: Pass correct context into get_block_categories

[Mamaduka]

Site Editor passes global $post as a context when setting up block categories. Instead, it should pass $block_editor_context, since global $post is null in this file.

To reproduce:

<?php
add_filter( 'block_categories_all', function( $categories, $context ) {
        error_log( var_export( $context instanceof WP_Block_Editor_Context, true ) );

        return $categories;
}, 10, 2 );

Expected:

The example above should log true twice.

Actual:

Logs true and false.

Note: The second log represents the get_block_categories call when setting up the categories. The first comes from get_block_editor_settings, where context is correctly set.

Passes correct context into get_block_categories and removes $post global from the site-editor.php file.

Trac ticket: https://core.trac.wordpress.org/ticket/56284

cc @gziolo

Thank you for working on it and the ping @Mamaduka. It looks like a step in the right direction. It feels like there are more places where the same issue might exist already, or it might get exposed in the future when the context passed on different screens further evolves.

[gziolo]

To clarify, with the patch applied, the filter presented in the description runs only once and it has the correct block context provided.

Thanks for the feedback and review, @gziolo!

[gziolo]

In 53784:

Site Editor: Pass correct context into get_block_categories

Site Editor passed incorrectly global $post as a context when setting up block categories. Instead, it should pass $block_editor_context, since global $post is null in this file.

Props Mamaduka.
Fixes #56284.

Committed with https://core.trac.wordpress.org/changeset/53784.