Themes: Check both parent and child themes for a `theme.json` file.

This updates `WP_Theme_JSON_Resolver::theme_has_support()` to properly check for a `theme.json` file in both parent and child themes when determining whether a theme supports block templates.

Follow up to [52077].

Props Mamaduka.
Fixes #54401.
Built from https://develop.svn.wordpress.org/trunk@52181


git-svn-id: http://core.svn.wordpress.org/trunk@51773 1a063a9b-81f0-0310-95a4-ce76da25c4cd

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

@@ -363,7 +363,10 @@ class WP_Theme_JSON_Resolver {
 	 */
 	public static function theme_has_support() {
 		if ( ! isset( self::$theme_has_support ) ) {
-			self::$theme_has_support = is_readable( self::get_file_path_from_theme( 'theme.json' ) );
+			self::$theme_has_support = (
+				is_readable( self::get_file_path_from_theme( 'theme.json' ) ) ||
+				is_readable( self::get_file_path_from_theme( 'theme.json', true ) )
+			);
 		}
 
 		return self::$theme_has_support;

wp-includes/version.php

@@ -16,7 +16,7 @@
  *
  * @global string $wp_version
  */
-$wp_version = '5.9-alpha-52180';
+$wp_version = '5.9-alpha-52181';
 
 /**
  * Holds the WordPress DB revision, increments when changes are made to the WordPress DB schema.