Compatibility fixes for PHP 8.1 #19143

Description:

This PR will run the AllTests on PHP 8.1 and includes

• various fixes for deprecation notices on PHP 8.1
• couple of test fixes for PHP 8.1
• fix for possible problems for PHP 8.1 using MySQLi connector
• fix for PHP 8.0.17 / 8.0.18 & 8.1.4 / 8.1.5 using zlib.output_compression = On

Review

• [ ] Functional review done
• [ ] Potential edge cases thought about (behavior of the code with strange input, with strange internal state or possible interactions with other Matomo subsystems)
• [ ] Usability review done (is anything maybe unclear or think about anything that would cause people to reach out to support)
• [ ] Security review done
• [ ] Wording review done
• [ ] Code review done
• [ ] Tests were added if useful/possible
• [ ] Reviewed for breaking changes
• [ ] Developer changelog updated if needed
• [ ] Documentation added if needed
• [ ] Existing documentation updated if needed

@justinvelluppillai Yes. I thought about that as well. The "problem" is that we therefor need to patch the Zend_Db classes, which I'd prefer not to do. Would be better to get rid of them at some point and introduce a new database library or write something own...