Blaze: only enqueue script in post editor

Fixes #28184

1. We do not need Blaze in the site editor, since we cannot promote specific posts from there.
2. The Blaze panel relies on @wordpress/editor, which we cannot use in the site editor or the widget editor.
3. When we enqueue the Blaze panel in the site editor or the widget editor, we run into this issue: #20357. This causes Fatal errors just like the one we experienced and worked around in #21763.

To solve this issue, we switch to using the admin_enqueue_scripts hook to decide whether when to enqueue our script. It allows us to conditionally enqueue the file based on the page we're on, which is something the enqueue_block_editor_assets hook does not allow yet.

projects/packages/blaze/changelog/fix-fatal-site-editor-blaze

@@ -0,0 +1,4 @@
+Significance: patch
+Type: fixed
+
+Do not load the Blaze panel in the site editor or the widget editor.

projects/packages/blaze/src/class-blaze.php

@@ -43,7 +43,7 @@ public function register() {
 		if ( ! did_action( 'jetpack_on_blaze_init' ) ) {
 			if ( self::should_initialize() ) {
 				add_filter( 'post_row_actions', array( $this, 'jetpack_blaze_row_action' ), 10, 2 );
-				add_action( 'enqueue_block_editor_assets', array( $this, 'enqueue_block_editor_assets' ) );
+				add_action( 'admin_enqueue_scripts', array( $this, 'enqueue_block_editor_assets' ) );
 			}
 
 			/**
@@ -133,8 +133,19 @@ public function jetpack_blaze_row_action( $post_actions, $post ) {
 
 	/**
 	 * Enqueue block editor assets.
+	 *
+	 * @param string $hook The current admin page.
 	 */
-	public function enqueue_block_editor_assets() {
+	public function enqueue_block_editor_assets( $hook ) {
+		/*
+		 * We do not want (nor need) Blaze in the site editor or the widget editor, only in the post editor.
+		 * Enqueueing the script in those editors would cause a fatal error.
+		 * See #20357 for more info.
+		 */
+		if ( ! in_array( $hook, array( 'post.php', 'post-new.php' ), true ) ) {
+			return;
+		}
+
 		Assets::register_script(
 			'jetpack-promote-editor',
 			'../build/editor.js',