Global Styles: Improve performance of WP_Theme_JSON::get_merged_data …

…method.

In the WordPress 6.1 cycle, WP_Theme_JSON_Resolver::get_merged_data method has become a hot path that is called many times. By improving small things that are repeated multiple times, we get more performance wins.
This commit reduces the number of calls of the low-level WP_Theme_JSON->merge method, with the corresponding performance improvements.

Props oandregal, aristath, mukeshpanchal27.
See #56467.

git-svn-id: https://develop.svn.wordpress.org/trunk@54517 602fd350-edb4-49c9-b593-d223f7449a82

src/wp-includes/class-wp-theme-json-resolver.php

@@ -548,8 +548,7 @@ public static function get_merged_data( $origin = 'custom' ) {
 			_deprecated_argument( __FUNCTION__, '5.9.0' );
 		}
 
-		$result = new WP_Theme_JSON();
-		$result->merge( static::get_core_data() );
+		$result = static::get_core_data();
 		$result->merge( static::get_block_data() );
 		$result->merge( static::get_theme_data() );