A new JIT engine for PHP-8.4/9

Hi internals, I'm glad to present a new JIT engine that is going to be used in the next major PHP version. Now it's a real optimizing compiler with Intermediate Representation similar to Java HotSpot server compiler. It makes a base for future improvements and eliminates many low-level details of the existing PHP JIT. Instead of supporting assembler code for different CPUs, now PHP generates a single IR and passes it to a PHP-independent JIT engine. The old JIT implementation is going to be kept for a while. Everybody are welcome to take a look over tne code https://github.com/php/php-src/pull/12079 Thanks. Dmitry.