KSES: Add object-position to the list of safe CSS properties.

This resolves an issue with the Cover block, where the `object-position` property is removed from the content when a non-admin user saves the post, leading to block recovery loop.

Props Mamaduka, aristath.
Fixes #52961.

git-svn-id: https://develop.svn.wordpress.org/trunk@50634 602fd350-edb4-49c9-b593-d223f7449a82

src/wp-includes/kses.php

@@ -2171,6 +2171,7 @@ function safecss_filter_attr( $css, $deprecated = '' ) {
 	 * @since 5.3.0 Added support for `grid`, `flex` and `column` layout properties.
 	 *              Extend `background-*` support of individual properties.
 	 * @since 5.3.1 Added support for gradient backgrounds.
+	 * @since 5.7.1 Added support for `object-position`.
 	 *
 	 * @param string[] $attr Array of allowed CSS attributes.
 	 */
@@ -2284,6 +2285,7 @@ function safecss_filter_attr( $css, $deprecated = '' ) {
 			'direction',
 			'float',
 			'list-style-type',
+			'object-position',
 			'overflow',
 			'vertical-align',
 		)