Bump to PHP 8.0+

PHP 7.4 was end of life November 2022, it's time to bump to PHP 8 standard 🎉

- updated starting code to PHP 8 standard
- upgraded tooling (code quality, static analysis) to the latest versions
- tested with PHP 8.0, 8.1 and 8.2
   - the fixture is working
   - the example test is failing, as expected
   - code quality is as expected
   - static analysis is ok

php/.gitignore

@@ -1,6 +1,6 @@
-/.idea 
-/report.xml 
-/.phpstorm.meta.php 
-/.phpunit.result.cache
+/.idea
 /build
-/vendor
+/vendor
+/.editorconfig
+/.phpunit.result.cache
+/composer.lock