Code Modernization: Fix reserved keyword and parameter name mismatches for parent/child classes in Walker::start_el().

In the parent class, renames the parameter `$object` to `$data_object`.

Why? `object` is a PHP reserved keyword.

In each child class: renames the corresponding parameter to match the parent's method signature.

Why? 

PHP 8 introduces the ability to pass named arguments to function/method calls. This means the child and parent method signatures (i.e. parameter names) need to match.

Changes for readability:

- `@since` clearly specifies the original parameter name and its new name as well as why the change happened.

- in methods longer than a single line, the generic parameter is reassigned to the original parameter restoring it for context for use within the method. An inline comment is added to explain why this reassignment is made.

- in cases where the original parameter name was too generic, renamed (when reassigning) to a more descriptive name for use within the method.

Follow-up to [7737], [8900], [8970], [14248], [15077], [16100], [25642], [25644], [37051], [37054], [37056], [46271], [47189].

Props jrf, hellofromTonya, sergeybiryukov, azaozz, desrosj, johnbillion.
See #51553.
Built from https://develop.svn.wordpress.org/trunk@51739


git-svn-id: http://core.svn.wordpress.org/trunk@51347 1a063a9b-81f0-0310-95a4-ce76da25c4cd

wp-includes/class-walker-page.php

@@ -93,14 +93,18 @@ class Walker_Page extends Walker {
 	 *
 	 * @see Walker::start_el()
 	 * @since 2.1.0
+	 * @since 5.9.0 Renamed `$page` to `$data_object` to match parent class for PHP 8 named parameter support.
 	 *
 	 * @param string  $output       Used to append additional content. Passed by reference.
-	 * @param WP_Post $page         Page data object.
+	 * @param WP_Post $data_object  Page data object.
 	 * @param int     $depth        Optional. Depth of page. Used for padding. Default 0.
 	 * @param array   $args         Optional. Array of arguments. Default empty array.
 	 * @param int     $current_page Optional. Page ID. Default 0.
 	 */
-	public function start_el( &$output, $page, $depth = 0, $args = array(), $current_page = 0 ) {
+	public function start_el( &$output, $data_object, $depth = 0, $args = array(), $current_page = 0 ) {
+		// Restores the more descriptive, specific name for use within this method.
+		$page = $data_object;
+
 		if ( isset( $args['item_spacing'] ) && 'preserve' === $args['item_spacing'] ) {
 			$t = "\t";
 			$n = "\n";