Editor: Optimize `wp_get_block_css_selector` to remove `array_merge` calls for better performance.

Some block themes like TT3 use `wp_get_block_css_selector` to determine a CSS selector based on block type and other parameters.  However, recent performance profiling indicated a bottleneck in `wp_get_block_css_selector`, particularly sections that utilize `array_merge`.  By slightly refactoring these sections, `array_merge` calls can be avoided which increases performance.

Props mukesh27, joemcgill, daxelrod, tabrisrp.
Fixes #59178.
Built from https://develop.svn.wordpress.org/trunk@56457


git-svn-id: http://core.svn.wordpress.org/trunk@55969 1a063a9b-81f0-0310-95a4-ce76da25c4cd

wp-includes/global-styles-and-settings.php

@@ -539,7 +539,7 @@ function wp_get_block_css_selector( $block_type, $target = 'root', $fallback = f
 		// Prefer the selectors API if available.
 		if ( $has_selectors ) {
 			// Look for selector under `feature.root`.
-			$path             = array_merge( $target, array( 'root' ) );
+			$path             = array( current( $target ), 'root' );
 			$feature_selector = _wp_array_get( $block_type->selectors, $path, null );
 
 			if ( $feature_selector ) {
@@ -553,7 +553,7 @@ function wp_get_block_css_selector( $block_type, $target = 'root', $fallback = f
 		}
 
 		// Try getting old experimental supports selector value.
-		$path             = array_merge( $target, array( '__experimentalSelector' ) );
+		$path             = array( current( $target ), '__experimentalSelector' );
 		$feature_selector = _wp_array_get( $block_type->supports, $path, null );
 
 		// Nothing to work with, provide fallback or null.

wp-includes/version.php

@@ -16,7 +16,7 @@
  *
  * @global string $wp_version
  */
-$wp_version = '6.4-alpha-56456';
+$wp_version = '6.4-alpha-56457';
 
 /**
  * Holds the WordPress DB revision, increments when changes are made to the WordPress DB schema.