[php-src] Issue #11218: Implement CHERI framework

Issue: https://github.com/php/php-src/issues/11218 Author: hexydec ### Description Recently at the CYBERUK23 conference, I went to a session about secure computing. A very interesting talk highlighting that 70% of all software vulnerabilities are rooted in buffer overflows. Rust is a language that was developed with memory management built in to prevent this class of vulnerabilities, but that does not address the huge corpus of C and C++ code out there. Most solutions currently are a bit cumbersome, and either require big code changes or have a detrimental effect on performance. Over the last 10 years, the University of Cambridge with support from Arm, Microsoft, Google and others have developed Capability Hardware Enhanced RISC Instructions (CHERI), a framework for preventing buffer overflows on C and C++. It requires minimal code changes (In the talk they said around 0.03%), and has a very small performance penalty, as the underlying code is implemented in around 300 instructions all together. Interestingly whilst there are around 40m+ lines of open source Rust code, there is actually now around 100m+ lines of open source C and C++ code adapted to be compiled with CHERI. Owing to the popularity of PHP, I thought this might be a useful tool to make it more secure. Read more here: [CHERI Frequently Asked Questions](https://www.cl.cam.ac.uk/research/security/ctsrd/cheri/cheri-faq.html)