Welcome PHP 8.0 RC 2 to the ports tree

There are many greater changes including:

• json is now part of core
• xmlrpc is removed
• More than 150 backward incompatible changes

Have a look at: https://github.com/php/php-src/blob/php-8.0.0RC2/UPGRADING

Reviewed by: ale, mfechner, Pascal Christen
Sponsored by: PHP Update Service
Differential Revision: https://reviews.freebsd.org/D26848