Code Modernization: Use `str_starts_with()` in `WP_Theme_JSON` class methods.

This aims to make the code more readable and consistent, as the function is already used extensively in core files.

WordPress core includes a polyfill for `str_starts_with()` on PHP < 8.0 as of WordPress 5.9.

Follow-up to [55703], [55959].

Props spacedmonkey.
Fixes #58012.
Built from https://develop.svn.wordpress.org/trunk@55987


git-svn-id: http://core.svn.wordpress.org/trunk@55499 1a063a9b-81f0-0310-95a4-ce76da25c4cd

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

@@ -3495,7 +3495,7 @@ class WP_Theme_JSON {
 		$prefix_len = strlen( $prefix );
 		$token_in   = '|';
 		$token_out  = '--';
-		if ( 0 === strpos( $value, $prefix ) ) {
+		if ( str_starts_with( $value, $prefix ) ) {
 			$unwrapped_name = str_replace(
 				$token_in,
 				$token_out,
@@ -3519,7 +3519,7 @@ class WP_Theme_JSON {
 		$prefix = 'var:';
 
 		foreach ( $tree as $key => $data ) {
-			if ( is_string( $data ) && 0 === strpos( $data, $prefix ) ) {
+			if ( is_string( $data ) && str_starts_with( $data, $prefix ) ) {
 				$tree[ $key ] = self::convert_custom_properties( $data );
 			} elseif ( is_array( $data ) ) {
 				$tree[ $key ] = self::resolve_custom_css_format( $data );

wp-includes/version.php

@@ -16,7 +16,7 @@
  *
  * @global string $wp_version
  */
-$wp_version = '6.3-alpha-55986';
+$wp_version = '6.3-alpha-55987';
 
 /**
  * Holds the WordPress DB revision, increments when changes are made to the WordPress DB schema.