Docs: Document the usage of globals in some functions.

This affects:
* `the_block_editor_meta_boxes()`
* `wp_generate_block_templates_export_file()`
* `WP_oEmbed_Controller::get_proxy_item()`

Follow-up to [44131], [48135], [51151], [53129].

Props krunal265.
Fixes #57082.

git-svn-id: https://develop.svn.wordpress.org/trunk@54831 602fd350-edb4-49c9-b593-d223f7449a82

src/wp-admin/includes/post.php

@@ -2210,6 +2210,10 @@ function get_block_editor_server_block_settings() {
  * Renders the meta boxes forms.
  *
  * @since 5.0.0
+ *
+ * @global WP_Post   $post           Global post object.
+ * @global WP_Screen $current_screen WordPress current screen object.
+ * @global array     $wp_meta_boxes
  */
 function the_block_editor_meta_boxes() {
 	global $post, $current_screen, $wp_meta_boxes;