Implement xxHash for non-cryptographic use-cases

Problem/Motivation

PHP 8.1 adds support for xxHash - a very fast, collision-resistant, non-crytographic hash.

We use a lot of hashes for non-crypto purposes, and our approach flip-flops between using weak non-crypto hashes like crc32, or mis-using cryptographic hashes to be 'correct'. xxHash means we don't need to flip-flop any more.

Steps to reproduce

Proposed resolution

Remaining tasks

Open sub-issues for each hash usage we want to change, including the recently added one in #2531564: Fix leaky and brittle container serialization solution → .

User interface changes

API changes

Data model changes

Release notes snippet