devel/pear-htmlpurifier: update to 4.15.0 for support PHP 8+

Runtime errors with PHP 8.1:
"Generates a PHP fatal error: autoload() is no longer supported, use
spl_autoload_register()"
"Generates a PHP fatal error: Array and string offset access syntax with
curly braces is no longer supported"

Changelog: https://github.com/ezyang/htmlpurifier/blob/master/NEWS
4.15.0, released 2022-09-18
! PHP 8.1 and 8.2 support, esp. fixes for deprecation warnings.

PR: 272938 272939
Approved by: adamw (mentor)
Differential Revision: https://reviews.freebsd.org/D41323
MFH: 2023Q3