Code Modernization: Use instanceof instead of a comparison with get_class().

Includes adjusting external libraries which are no longer maintained externally.

Props jrf.
See #50767.

git-svn-id: https://develop.svn.wordpress.org/trunk@49194 602fd350-edb4-49c9-b593-d223f7449a82

src/wp-admin/includes/class-pclzip.php

@@ -1171,7 +1171,7 @@
     $this->privErrorReset();
 
     // ----- Look if the $p_archive is a PclZip object
-    if ((is_object($p_archive)) && (get_class($p_archive) == 'pclzip'))
+    if (is_object($p_archive) && $p_archive instanceof pclzip)
     {
 
       // ----- Duplicate the archive
@@ -1235,7 +1235,7 @@
     }
 
     // ----- Look if the $p_archive_to_add is a PclZip object
-    if ((is_object($p_archive_to_add)) && (get_class($p_archive_to_add) == 'pclzip'))
+    if (is_object($p_archive_to_add) && $p_archive_to_add instanceof pclzip)
     {
 
       // ----- Merge the archive