MDL-84154 libraries: Upgrade HTML Purifier to 4.18.0

The library comes with an advertised PHP 8.4 compatibility.

Signed-off-by: Daniel Ziegenberg <[email protected]>

lib/htmlpurifier/HTMLPurifier/ConfigSchema/schema/Core.RemoveBlanks.txt

@@ -0,0 +1,10 @@
+Core.RemoveBlanks
+TYPE: bool
+DEFAULT: false
+VERSION: 4.18
+--DESCRIPTION--
+<p>
+    If set to true, blank nodes will be removed. This can be useful for maintaining
+    backwards compatibility when upgrading from previous versions of PHP.
+</p>
+--# vim: et sw=4 sts=4