* Fix - Dev - Fix unit testin infrastructure.
* Fix - Dev - Remove default value from optional parameters that are followed by required parameters in functions/methods, since those are de-facto required and trigger a deprectation notice in PHP 8.
* Fix - Dev - Set PHP version to 7.2 in composer.json for compatibility with PHP 8.
* Tweak - WC 4.7 compatibility.
* Tweak - WP 5.5 compatibility.