Upgrade/Install: Pass stored credentials to WP_Filesystem() where appropriate.

With the introduction of temporary backups of plugins and themes before updating, a new Site Health test was added to verify that plugin and theme temporary backup directories are writable or can be created.

When using a non-direct filesystem, the Site Health test did not include the required credentials, leading to a fatal error as the connection was not initialized properly.

This commit attemps to use the stored credentials if available, and displays a message otherwise.

Includes a similar fix in a function that performs a cleanup of the temporary backup directory.

Follow-up to [55720].

Props utsav72640, rajinsharwar, costdev, mukesh27, peterwilsoncc, audrasjb, SergeyBiryukov.
See #58940.
Built from https://develop.svn.wordpress.org/trunk@56341


git-svn-id: http://core.svn.wordpress.org/trunk@55853 1a063a9b-81f0-0310-95a4-ce76da25c4cd

wp-includes/version.php

@@ -16,7 +16,7 @@
  *
  * @global string $wp_version
  */
-$wp_version = '6.4-alpha-56339';
+$wp_version = '6.4-alpha-56341';
 
 /**
  * Holds the WordPress DB revision, increments when changes are made to the WordPress DB schema.