Block Types: Add metadata global attribute.

Add a new global attribute (i.e. an attribute that can be added to all and any blocks) called `metadata`. This is required for use cases such as allowing the user to assign custom names to blocks, or for making Block Hooks work with user-modified templates/parts/patterns (#59646).

Props Mamaduka, gziolo, get_dave.
Fixes #59797.

git-svn-id: https://develop.svn.wordpress.org/trunk@57068 602fd350-edb4-49c9-b593-d223f7449a82

src/wp-includes/class-wp-block-type.php

@@ -242,11 +242,13 @@ class WP_Block_Type {
 	/**
 	 * Attributes supported by every block.
 	 *
-	 * @since 6.0.0
+	 * @since 6.0.0 Added `lock`.
+	 * @since 6.5.0 Added `metadata`.
 	 * @var array
 	 */
 	const GLOBAL_ATTRIBUTES = array(
-		'lock' => array( 'type' => 'object' ),
+		'lock'     => array( 'type' => 'object' ),
+		'metadata' => array( 'type' => 'object' ),
 	);
 
 	/**