Script Modules API: Add import map polyfill for older browsers

Syncs the changes from https://github.com/WordPress/gutenberg/pull/58263. Adds a polyfill to make import maps compatible with unsported browsers (https://caniuse.com/import-maps).

Fixes #60348.
Props cbravobernal, jorbin, luisherranz, jonsurrell.



git-svn-id: https://develop.svn.wordpress.org/trunk@57492 602fd350-edb4-49c9-b593-d223f7449a82

src/wp-includes/script-loader.php

@@ -96,6 +96,7 @@ function wp_default_packages_vendor( $scripts ) {
 		'lodash',
 		'wp-polyfill-fetch',
 		'wp-polyfill-formdata',
+		'wp-polyfill-importmap',
 		'wp-polyfill-node-contains',
 		'wp-polyfill-url',
 		'wp-polyfill-dom-rect',
@@ -120,6 +121,7 @@ function wp_default_packages_vendor( $scripts ) {
 		'wp-polyfill-object-fit'      => '2.3.5',
 		'wp-polyfill-inert'           => '3.1.2',
 		'wp-polyfill'                 => '3.15.0',
+		'wp-polyfill-importmap'       => '1.8.2',
 	);
 
 	foreach ( $vendor_scripts as $handle => $dependencies ) {