Code Quality: Restore trunk hooks removed during rebase

Fix stale changes in default-filters.php that were carried over from
the old branch during the rewrite. Restores the Connectors API init
hook, login_head resource hints action, wp_default_styles hook for
classic theme block styles, and admin_init hook for collaboration
setting injection.

Author: josephfusco

src/wp-includes/default-filters.php

@@ -385,7 +385,7 @@
 
 // Login actions.
 add_action( 'login_head', 'wp_robots', 1 );
-add_filter( 'login_head', 'wp_resource_hints', 8 );
+add_action( 'login_head', 'wp_resource_hints', 8 );
 add_action( 'login_head', 'wp_print_head_scripts', 9 );
 add_action( 'login_head', 'print_admin_styles', 9 );
 add_action( 'login_head', 'wp_site_icon', 99 );
@@ -540,6 +540,9 @@
 add_action( 'wp_abilities_api_categories_init', 'wp_register_core_ability_categories' );
 add_action( 'wp_abilities_api_init', 'wp_register_core_abilities' );
 
+// Connectors API.
+add_action( 'init', '_wp_connectors_init', 15 );
+
 // Sitemaps actions.
 add_action( 'init', 'wp_sitemaps_get_server' );
 
@@ -605,7 +608,7 @@
 add_action( 'enqueue_block_assets', 'wp_enqueue_classic_theme_styles' );
 add_action( 'enqueue_block_assets', 'wp_enqueue_registered_block_scripts_and_styles' );
 add_action( 'enqueue_block_assets', 'enqueue_block_styles_assets', 30 );
-add_action( 'init', 'wp_load_classic_theme_block_styles_on_demand', 8 ); // Must happen before register_core_block_style_handles() at priority 9.
+add_action( 'wp_default_styles', 'wp_load_classic_theme_block_styles_on_demand', 0 ); // Must happen before wp_default_styles() and register_core_block_style_handles().
 /*
  * `wp_enqueue_registered_block_scripts_and_styles` is bound to both
  * `enqueue_block_editor_assets` and `enqueue_block_assets` hooks
@@ -797,7 +800,7 @@
 add_action( 'init', '_wp_register_default_font_collections' );
 
 // Collaboration.
-add_action( 'enqueue_block_editor_assets', 'wp_collaboration_inject_setting' );
+add_action( 'admin_init', 'wp_collaboration_inject_setting' );
 
 // Add ignoredHookedBlocks metadata attribute to the template and template part post types.
 add_filter( 'rest_pre_insert_wp_template', 'inject_ignored_hooked_blocks_metadata_attributes' );