Theme JSON Resolver: remove theme json merge in resolve_theme_file_uris

This commit affects `WP_Theme_JSON_Resolver::resolve_theme_file_uris()`.

When setting resolved URIs in an incoming theme json object, this commit removes the unnecessary call to `WP_Theme_JSON->merge()`. 

Why? `WP_Theme_JSON_Resolver::resolve_theme_file_uris()` only needs to set values for paths in the raw theme json object. It can then return a new theme object based on the updated JSON source. There's no need for a full and possibly expensive merge.

Follow-up to [61588].

Props ramonopoly, aaronrobertshaw, andrewserong.
Fixes #62329.



git-svn-id: https://develop.svn.wordpress.org/trunk@59338 602fd350-edb4-49c9-b593-d223f7449a82

Author: ramonjd

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

@@ -933,18 +933,14 @@ public static function resolve_theme_file_uris( $theme_json ) {
 			return $theme_json;
 		}
 
-		$resolved_theme_json_data = array(
-			'version' => WP_Theme_JSON::LATEST_SCHEMA,
-		);
+		$resolved_theme_json_data = $theme_json->get_raw_data();
 
 		foreach ( $resolved_urls as $resolved_url ) {
 			$path = explode( '.', $resolved_url['target'] );
 			_wp_array_set( $resolved_theme_json_data, $path, $resolved_url['href'] );
 		}
 
-		$theme_json->merge( new WP_Theme_JSON( $resolved_theme_json_data ) );
-
-		return $theme_json;
+		return new WP_Theme_JSON( $resolved_theme_json_data );
 	}
 
 	/**