Extend "At a Glance" widget support to independent content blocks

[himanshupathak95]

Trac ticket: https://core.trac.wordpress.org/ticket/26571

This PR resolves long-standing extensibility limitations within the "At a Glance" dashboard widget. It introduces targeted, enhancements to the widget's render pipeline, enabling developers to natively style existing items and append entirely new structural lists.

• Modified the $elements loop in wp_dashboard_right_now() (inside src/wp-admin/includes/dashboard.php) to accept an associative array structure with class and content keys.
• Ensures strict backward compatibility by defaulting to plain string parsing for array elements containing just HTML strings.
• Introduced a dedicated action hook immediately following the termination of the primary <ul>. This directly fulfills the ticket's secondary request to support "multiple lists," enabling developers to cleanly inject secondary lists or visual separators before the widget's metadata footer.

Screenshots

Before

After

Code Snippet Used -

add_filter( 'dashboard_glance_items', 'test_dashboard_glance_items_filter' );
function test_dashboard_glance_items_filter( $items ) {
	$items[] = '<a href="#">Custom Item Without Class</a>';
	return $items;
}

add_filter( 'dashboard_glance_items', 'test_dashboard_glance_items_hack' );
function test_dashboard_glance_items_hack( $items ) {
	$items[] = '</li><li class="custom-class-hack"><a href="#">Hacked Class Item</a>';
	return $items;
}

add_filter( 'dashboard_glance_items', 'test_dashboard_glance_items_array' );
function test_dashboard_glance_items_array( $items ) {
	$items[] = array(
		'class'   => 'new-custom-class',
		'content' => '<a href="#">New Array Class Item</a>',
	);
	return $items;
}

add_action( 'admin_head', 'test_dashboard_glance_items_css' );
function test_dashboard_glance_items_css() {
	echo '<style type="text/css">
		#dashboard_right_now .new-custom-class a:before {
			content: "\f348" !important; /* Dashicon dashicons-info */
			color: #0073aa;
		}
		#dashboard_right_now .new-custom-class {
			font-weight: bold;
		}
	</style>';
}

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