Centralize safe_style_css usages. (#36280)

lib/compat.php

@@ -186,6 +186,7 @@ function gutenberg_safe_style_attrs( $attrs ) {
 	$attrs[] = 'border-top-right-radius';
 	$attrs[] = 'border-bottom-right-radius';
 	$attrs[] = 'border-bottom-left-radius';
+	$attrs[] = 'filter';
 
 	return $attrs;
 }

lib/global-styles.php

@@ -215,7 +215,6 @@ function gutenberg_global_styles_filter_post( $content ) {
  */
 function gutenberg_global_styles_kses_init_filters() {
 	add_filter( 'content_save_pre', 'gutenberg_global_styles_filter_post' );
-	add_filter( 'safe_style_css', 'gutenberg_global_styles_include_support_for_duotone', 10, 2 );
 }
 
 /**
@@ -289,18 +288,6 @@ function gutenberg_global_styles_include_support_for_wp_variables( $allow_css, $
 	return ! ! preg_match( '/^var\(--wp-[a-zA-Z0-9\-]+\)$/', trim( $parts[1] ) );
 }
 
-/**
- * This is for using kses to test user data.
- *
- * @param array $atts Allowed CSS property names, according to kses.
- *
- * @return array The new allowed CSS property names.
- */
-function gutenberg_global_styles_include_support_for_duotone( $atts ) {
-	$atts[] = 'filter';
-	return $atts;
-}
-
 // The else clause can be removed when plugin support requires WordPress 5.8.0+.
 if ( function_exists( 'get_block_editor_settings' ) ) {
 	add_filter( 'block_editor_settings_all', 'gutenberg_experimental_global_styles_settings', PHP_INT_MAX );