Allow users who don't have edit_posts capability to edit attachment metadata

edit_attachment_meta.php

<?php
/**
 * Allow users who don't have edit_posts capability to edit attachment metadata.
 * From @grapplerulrich on https://core.trac.wordpress.org/ticket/19834#comment:42
 */
add_filter( 'register_post_type_args', function( $args, $post_type ) {
    if ( 'attachment' === $post_type ) {
        $args['capabilities']['edit_posts']   = 'upload_files';
        $args['capabilities']['upload_files'] = 'upload_files';
    }
    return $args;
}, 10, 2 );