Editor: Fix opinionated block styles loading in editor

Related changes in Gutenberg: WordPress/gutenberg#40937.

Backport for WordPress 6.0 RC 4.

Props jffng.
See #55567.



git-svn-id: https://develop.svn.wordpress.org/trunk@53419 602fd350-edb4-49c9-b593-d223f7449a82

src/wp-includes/block-editor.php

@@ -309,10 +309,13 @@ function _wp_get_iframed_editor_assets() {
 	$style_handles  = array(
 		'wp-block-editor',
 		'wp-block-library',
-		'wp-block-library-theme',
 		'wp-edit-blocks',
 	);
 
+	if ( current_theme_supports( 'wp-block-styles' ) ) {
+		$style_handles[] = 'wp-block-library-theme';
+	}
+
 	if ( 'widgets.php' === $pagenow || 'customize.php' === $pagenow ) {
 		$style_handles[] = 'wp-widgets';
 		$style_handles[] = 'wp-edit-widgets';