[php-src] Issue #7863: Replace Libxml2 by Gumbo or Lexbor for HTML parsing

Issue: https://github.com/php/php-src/issues/7863 Comment Author: cmb69 On further consideration, I see no way to actually replace libxml. It's not only about the userland code, but also about other extensions which are using exported ext/libxml functionality. Instead, alternative DOM etc. extensions. could be the way to go, but these should start out as external extensions, live in PECL for a while, and then they could be considered for bundling into php-src. Consider to write to the [PECL developer mailing list](https://pecl.php.net/support.php) to move this forward.