Editor: Add a fallback to WP_Block_Styles_Registry if the label is missing.

Both `name` and `label` properties are required when registering a block style. If the label is missing, assign `name` as the value for the `label`, to ensure the property is defined. This avoids a PHP warning in such case.

Props poena, Rahmohn, aaronrobertshaw, audrasjb, rinkalpagdar.
Fixes #52592.




git-svn-id: https://develop.svn.wordpress.org/trunk@59760 602fd350-edb4-49c9-b593-d223f7449a82

Author: audrasjb

src/wp-includes/class-wp-block-styles-registry.php

@@ -93,6 +93,11 @@ public function register( $block_name, $style_properties ) {
 		$block_style_name = $style_properties['name'];
 		$block_names      = is_string( $block_name ) ? array( $block_name ) : $block_name;
 
+		// Ensure there is a label defined.
+		if ( empty( $style_properties['label'] ) ) {
+			$style_properties['label'] = $block_style_name;
+		}
+
 		foreach ( $block_names as $name ) {
 			if ( ! isset( $this->registered_block_styles[ $name ] ) ) {
 				$this->registered_block_styles[ $name ] = array();